Once upon a time, Love Island contestant Adam Collard would simply have been called a player. His knack for pitting young women against each other, which provided much of the drama on this year’s series of the dating reality show, might well have been controversial; he might conceivably have been accused of vanity, for flashing his six-pack. But what was new and striking this summer was the furious debate among viewers over whether he could fairly be called a narcissist.

A century after Freud wrote his essay On Narcissism, identifying a form of self-adoration prompted by viewing oneself as an object of sexual desire, the term has filtered right down from psychology textbooks into casual everyday conversation. Like “gaslighting” – which evolved from a reference to a George Cukor film, to a form of emotional abuse identified by domestic violence specialists, to a word flung around with pretty wild abandon – its meaning has stretched sometimes to breaking point along the way. But it clearly fills a contemporary need.

Narcissists basically behave like four-year-olds. It’s all about them

“It’s a buzzword,” says Marianne Vicelich, author of the self-help book Destruction: Free Yourself From the Narcissist. “Every time you have dinner with a few girlfriends someone uses the term – their boss is a narcissist, or their husband, or their ex, or their mother.”

The Facebook group Knowing a Narcissist has built up a staggering 400,000 likes, with followers endlessly posting about the strains of dealing with a self-obsessed parent or partner. In her autobiography My Thoughts Exactly, Lily Allen describes her comedian father Keith as “cold and narcissistic”, too wrapped up in his own hedonistic life to spend much time with her.

Vicelich, a prolific author of self-help books, thinks that’s where young women are picking up the term. “Women are becoming a lot more educated when it comes to relationships,” she says. But it might also have something to do with psychologists openly speculating that Donald Trump might have narcissistic personality disorder, a clinical condition involving grandiose behaviour, fantasies about one’s own power and attractiveness, craving for admiration, and unwillingness to empathise with others (other presumed sufferers include Saddam Hussein).

The term is also increasingly being used against young women, accused of overindulging in all kinds of navel-gazing, from the cult of “self-care” (taking time out to cosset yourself) to compulsive posting of selfies. According to the American psychologists Jean Twenge and Keith Campbell in their book The Narcissism Epidemic: Living in the Age of Entitlement, social media along with other factors, from indulgent parenting to a highly individualistic culture, risks creating a generation excessively wrapped up in itself. But is this really a new phenomenon, or merely the latest expression of a phenomenon as old as human nature?

Mirror, mirror: we now seem to need to document our every waking minute. Photograph: Stefano Oppo/Getty Images

The original myth of Narcissus, the beautiful young man whose punishment from the gods was to fall so in love with his own reflection in a pool of water that he couldn’t bear to leave it, is on one level a warning against vanity; but it’s also a cautionary tale about isolation, because the cruelty of Narcissus’s punishment is that it cuts him off completely from other living human beings.

In small doses, narcissism can be a good thing; or at least, better than a crippling lack of self-esteem. Research at Queen’s University Belfast suggests narcissists score better in exams than other measures of their intelligence would suggest they should. In careers requiring confident judgement under pressure, such as finance or politics, a strong sense of self-belief could well be advantageous. But it becomes counter-productive when not tempered by respect for the views of others, and it’s this inability to feel compassion, empathy, or even much curiosity about others that distinguishes the truly narcissistic from the merely vain.

As Vicelich writes in her book, for narcissists “everything is about them and belongs to them”. They don’t recognise personal boundaries, hog conversations, crave constant validation and take criticism extremely badly. “They basically behave like four-year-olds: it’s all about them,” she says. “They want your attention, they need things right now – it’s all about instant gratification – and they really have an undeveloped sense of self.” They can be charming, flirtatious company. But they typically see others largely as extensions of themselves and can be controlling, cruel or critical of anyone they feel reflects badly on them. Loved ones willing to feed their egos are known in self-help lexicon as their “supply” – attention is to narcissists as drugs are to addicts – and that supply needs constant replenishing. What’s changed in a decade is the ease of getting a fix.

If you attack them, you wound their fragile egos and that’s not good

Facebook, Instagram, YouTube and Twitter all supply attention-seekers with oodles of what they crave, in the satisfyingly measurable form of likes and shares. With its heavily filtered images of perfect abs and perfect lives, Insta is most often accused of harbouring narcissists, but it’s striking how many Twitter trolls would also fit the definition of a craving to be noticed plus indifference to pain caused. (Katie Hopkins once admitted that she’d considered whether she might be a psychopath, narcissist or autistic but decided none of the labels fitted.)

In their book, Twenge and Campbell use questionnaires filled out by generations of college students to show a marked rise in scores on the so-called Narcissistic Personality Index since the 1980s, especially in women. It’s a contested area, with some questioning whether narcissism is even a recognisable condition given how loosely it’s defined, and middle-aged complaints about the young being selfish are certainly not new (back in the 1970s it was baby boomers who were being dismissed as “Generation Me”).

But if each of us lies somewhere on a spectrum between humble self-effacement and monstrous egotism, then we can be shifted slightly towards one end or another by changes in what’s considered socially acceptable behaviour, says Agnieszka Golec de Zavala, senior lecturer in psychology at Goldsmiths. “It’s possible that we have a norm, a permissive norm towards narcissism now, and that’s why this trait is more visible. That means societies are more narcissistic because people feel freer [to express it].” Social media or reality TV might, in other words, have simply provided new outlets for something that was always there, legitimising the idea that we’re all special enough to document our every waking minute or that the world urgently needs our take on the final episode of The Bodyguard. Yet for a supposedly self-absorbed generation, it’s striking how ambivalent millennials are becoming about social media.

Jamie Jewitt is a former model who was one half of Love Island’s runner-up couple last year, with his girlfriend Camilla Thurlow. He has more than 831,000 followers on Instagram and 128,000 on Twitter, and since leaving the show has filmed documentaries for the BBC and recorded a TED talk. He has all the attention any self-respecting millennial could desire, yet is about to start giving talks in schools about the perils of overdoing social media. If tomorrow he was told that he could no longer use it, how would he feel? “For me, I know it would be a huge relief,” he admits. “The annoying thing is that it’s necessary at the moment. It’s a huge avenue to get publicity for the work that we are doing and it’s always going to be a very handy tool for that, but it’s a bittersweet thing. It’s a necessary evil, put it like that.”

Big baby: does Donald Trump have a narcissistic personality disorder? Photograph: Charlie Riedel/AP

Jewitt dates his discomfort back to his modelling days, when he was expected to upload a steady flow of unrealistically flattering pictures on Instagram as a showcase for prospective clients. “All of my model friends were doing what they were told, posting these images, becoming a bit self-absorbed and going down the rabbit hole. I refused to do it and I ended up losing out on work, but I had such conflicting feelings about it,” he says.

After Love Island, he was determined not to go back into that world; instead he and Camilla volunteered in a Greek refugee camp (she had been working for a mine-clearing charity before going on the show), and made a documentary about it. “I didn’t want to come out and end up living a life that was just a version of what I’d done before with modelling. It became such a fundamental thing, to have Insta and self-promote, and it was a dishonest way of living – you had to take pictures of yourself looking your best, just so the clients would see you as a viable tool to use to sell their products. It’s not real and it’s not healthy.”

Although 28-year-old Jewitt might not be your average reality TV contestant, his reservations about social media are fairly typical of his generation. A third of Generation Z have deleted accounts in the past year, with a fifth saying they wanted more privacy and couldn’t cope with the pressure to get attention, according to research by Origin, a Boston-based market research company. Private messaging circles like Snapchat and WhatsApp are overtaking public-facing platforms like Facebook and Twitter among the young. But if the generation raised on social media is increasingly wary of its impact on them, the generation who discovered it later in life is a different matter.

“Make America great again.” “Take back control.” “The people have had enough of experts.” What’s striking about the slogans adopted by Trump in the US and the Leave campaign in Britain is that they flatter the movement’s supporters as much as its leaders. They imply that the people are invariably smarter than anyone disagreeing with them, that they deserve to be in charge, that their natural greatness is being unfairly suppressed.

And whether deliberately or not, it’s a siren call to what’s known as collective narcissism, or an exaggerated love not of oneself but of one’s group. Collective narcissists aren’t personally grandiose – if anything they may feel individually powerless – but can be cultlike in their devotion to a national, religious or ideological identity with which they identify.

“Collective narcissists feel their group is threatened all the time, that others are after it. They’re prone to conspiratorial thinking,” explains Golec de Zavala, who specialises in researching the phenomenon. “Whenever they feel their group status is threatened, if they had it in their power, they would aggress against those who threaten it. Things that other people would not even notice or imagine are insulting, they would be hostile towards.”

On social media, de Zavala says, they tend to come across as “zealous” and persevere with arguments well after others have given up. And while her research shows they’re disproportionately likely to have voted for Trump in the US or Brexit in the UK, “it could be that on the left there are collective narcissists, too.” The cap is certainly a good fit not just for Brexiteers hellbent on crushing imagined saboteurs, or white men furiously objecting to Black History Month on the grounds that it doesn’t seem to be about them, but also perhaps for the posters of memes comparing Jeremy Corbyn to a persecuted Jesus. More disturbingly, the collective narcissist’s extreme intolerance for dissent might help explain why politicians in all parties now routinely face death threats over ideological stances taken.

In small doses, collective narcissism can foster a healthy sense of patriotism or pride. But it can turn ugly when supporters are encouraged to believe that their own group’s innate specialness isn’t being properly recognised and that rival groups are getting what’s rightfully theirs. What differentiates them from other protest movements, says de Zavala, is that they don’t just want equality but “special privilege”, or supremacy over everyone else.

“What I think is happening to us now worldwide is that this collective narcissistic construction of national identity became the norm,” she says. “It’s something that was marginalised and now is becoming mainstream and if you look at our research on collective narcissism, that’s a bad sign.”

The concept originates from the 1930s, when it was used to explain why people who lost their personal sense of self-worth in the depression began investing heavily in group identities instead, and the parallels with the 2008 crash are all too alarming. De Zavala started researching collective narcissism in part because she wondered if there was a way of curbing it early, bearing in mind where it ultimately led in the 1930s. One option, she thinks, might be channelling collective narcissists’ energies into constructive ways of boosting their group, such as voluntary work in their communities – essentially a twist on John F Kennedy’s “Ask not what your country can do for you” approach. But her research points towards tackling the fact that collective narcissists are generally dissatisfied with their lives. “If you make people experience self-transcendent emotions – such as gratitude or something that diminishes the importance of ego – we had experimental studies which showed that, especially among collective narcissists, it reduces prejudice.” In other words, the ability to focus on something bigger than yourself might have more profound social effects than we realise.

Taming the individual narcissist in your life, or indeed your Oval Office, may be harder given their indifference to others’ distress and their inability to take criticism. “If you attack them, that’s wounding their fragile egos, so that’s no good – in a relationship you just have to work around them,” says Marianne Vicelich. It is hard not to be reminded of how the White House insiders are described in Bob Woodward’s new book Fear: Trump in the White House, creeping around removing papers from Trump’s desk to stop him signing them rather than confronting him directly.

And if you can’t avoid dealing with a narcissistic parent or boss? Stand up for yourself, Vicelich says, remembering that their bombastic exteriors are often a defence against deep insecurity. “They’re not happy people. Once you realise their egos are so fragile and that what they’re saying is no reflection on you, you can start setting boundaries.”

The original Narcissus, it’s worth remembering, eventually died of sorrow at his lonely predicament. Perhaps the most underrated act of self-care in the modern world is the ability, just occasionally, to get over yourself.

• This article was amended on 9 October 2018 to correct a reference to the film Gaslight: George Cukor directed it, not Alfred Hitchcock.