These days, ‘creepy’ is a popular pejorative. From ‘Creepy Uncle Joe’ Biden’s hair-smelling antics to Justin Trudeau standing ‘too close’ to a tennis star, from the random dude who just slid into your direct messages to Zach Braff holding hands with a much-younger actress, many people are invoking creepiness as a factor, even a decisive one, in considerations about what is socially acceptable and even who is fit for political office. Creeps, it seems, are everywhere.

It’s a strange development. Why are we calling so many people, usually men, creepy? Despite the prevalence of the creepiness discourse, real research into the nature of creepiness is pretty new. It suggests that creepiness is related to disgust, which is an adaptive emotional response that helps to maintain a physical barrier between our bodies and potentially injurious external substances. Disgust assists us in policing the line between inside and outside our bodies, but also to create and maintain interpersonal and social borders. Physical reactions – such as the shudder response, nausea, and exclamations of ‘ew’, ‘icky’ and ‘gross’ – can be important ways of producing and transmitting commitments to social norms. Signalling disgust helps society maintain the integrity of taboos around sexuality, including paedophilia and incest.

Biologically, being grossed out by, for example, the idea of ingesting faeces makes sense: it keeps us from getting ill. Feeling ‘creeped out’ by a person or a social situation, however, is less straightforward. Creepiness is different from disgust in that it refers to a feeling of unease in the face of social liminality, particularly where sex and death are involved. We become uncomfortable when events don’t easily fit our expectations or transgress social rules. In a 2016 study, the psychologists Francis McAndrew and Sara Koehnke at Knox College in Illinois concluded that ‘creepiness is anxiety aroused by the ambiguity of whether there is something to fear or not and/or by the ambiguity of the precise nature of the threat’. Emotionally, creepiness helps us externalise our internal sense of confusion and uncertainty when presented with situations that are not easily categorised. Feeling ‘creeped out’ justifies our decision to shut down, rather than undertake the task of analysing ambiguously threatening situations. It is a form of cognitive paralysis indicating that we are unsure how to proceed.

Because women are more likely than men to experience physical and sexual threat in their daily lives, they are also more likely to judge others (usually men) to be creepy. Judgments of creepiness, however, are not necessarily reliable.

Conventional wisdom tells us to ‘trust our gut’, but researchers say that our gut is concerned more with regulating the boundaries of social mores than keeping us safe. In a 2017 Canadian study, female undergraduates were shown images of Caucasian male faces from three groups: emotionally neutral faces taken from an image bank; images judged ‘creepy’ in a pilot study; and images of criminals from America’s Most Wanted. They were then asked to rate the faces according to creepiness, trustworthiness and attractiveness. Across all three groups, there was a strong correlation between faces that participants considered trustworthy and attractive, and in some instances general attractiveness was negatively correlated with judgments of creepiness. Further, the faces taken from America’s Most Wanted were not rated as significantly more creepy than the neutral group. Participants made their creepiness assessments in seconds, and reported high degrees of confidence in their judgments.

Participants thought that, rather than describing behaviours, creepiness adhered to certain kinds of people and occupations. This is important.

Unkempt and dirty men, men with abnormal facial features, and men between the ages of 31-50 were all very likely to be rated creepy. Furthermore, creepiness was positively correlated both with the belief that the person held a sexual interest in the person making the social judgment, and with individuals who engaged in non-normative behaviours. This finding aligns with the McAndrew and Koehnke study, in which clowns, sex-shop owners and those interested in taxidermy were among the creepiest kinds of people.

So rather than reliably detecting danger, our internal ‘spidey sense’ often signals social difference or otherness. When we judge a situation or person creepy, we participate in shunning and social ostracism. Creepiness can prevent us from responding to the odd, the new or the peculiar with curiosity, interest and generosity of spirit.

The implicit answer to what we should do with creepy people (usually men) is embedded in the question: we should react to them with suspicion and social hostility. When we fail to do so and a stereotypically creepy person behaves violently, we then look back on the failure to create adequate distance with a ‘told you so’ attitude.

This was the legal position taken recently in a case for wrongful death against a grocery store in Maine. The civil lawsuit was brought by the husband of a woman who was murdered in the store by another regular, and reputedly creepy, customer. Although the offender in question ‘had an angry face, bulging eyes, and clenched jaw, exhibited taciturn behaviour, was seen shaking a couple of times’ and sometimes appeared to be ‘“on” something’, the judge said that the grocery store had not failed in its duty to safeguard shoppers from reasonably foreseeable third-party violence. However, the judge left open the question whether, in order to avoid risk, shop owners have a duty to exclude customers who appear creepy, but who don’t have a known history of violence.

As researchers warn, what most people intuit to be creepy aligns closely with the attributes of individuals and populations already on or beyond the boundaries of social acceptance. The mentally ill and disabled, the physically deformed, those with ticks or other abnormal movements or facial features, the impoverished and the homeless are all more likely to be judged creepy. With this knowledge, we need to guard against confirmation bias when perceived creeps actually do act in harmful ways. It might be tempting to use the story of the Maine grocery-store murder as evidence that creepy people are prone to violence. But we should probably remember what we have known for some time: that the homeless and mentally ill are far more vulnerable to acts of violence than they are threatening to the rest of us. In short, ‘we’ are far more likely to hurt the ‘creepy’ than they us.

What does this tell us about how we should think about creepiness when it comes to a co-worker, a politician or a celebrity? To date, little has been written about the social and psychological mechanisms that make #MeToo allegations compelling. But it has become common and acceptable to publicly evaluate and judge sexual conduct and experiences according to the capacious affective language of disgust. Today, sex that leaves a woman ‘feeling gross’, or sexually non-normative behaviour that reads as ‘creepy’, can be enough to cast a man out of polite society.

Much of the #MeToo movement purports to focus on bad behaviour; namely, the violation of the requirement of consent in sexual encounters. On its face, #MeToo discourse relies heavily on the supposedly clear line between consent and violation, where the trouble presented by ‘grey areas’ is understood to be fixable if only we better understood – and were more publicly aware of – the nature of consent. But for all the talk about the importance of consent, there is another slippery process at work under the surface. Here, the affective vector of creepiness allows us to express our discomfort with an age-gap relationship or a request for a masturbation audience, even in situations where consent is present.

Creepiness research shows us that our perceptual intuitions about people and situations are at least as important – and perhaps more important than – cognitive judgment based on bad conduct. The line between sex and assault – the line marked by consent – is just one place where evaluation occurs. A sexual encounter can be intensely creepy – and entirely legal.

But if we allow creepiness to stand in for principled normative assessment of the kinds of sex we want to hold up as socially valuable, it will be at the expense of historically sexually marginalised groups: the queers, the perverts, the BDSM community, and others who find joy and meaning in the sexually experimental. Perhaps, instead of spending so much energy excluding creeps, we should all turn our gaze inward and ask, in the words of Radiohead: ‘I’m a creep/I’m a weirdo/What the hell am I doing here?’