Imagine it is your birthday. You are 12 years old today and you have just been given your first guitar. Your dad extends it towards you like a newborn baby and you, glowing from the inside out, rest the body safely on your knee and clasp the neck with your gangly, inexperienced fingers. Your mum motions to take a picture, to preserve the moment forever. You soften your pre-teen grimace and lift up your free hand to throw the sign of the horns – a gesture you understand to be an expression of both hardness and passion. You extend your index and little finger, while holding the middle and ring fingers down with your thumb.

You are 12 years old, and you have just called your mum a cuck.

The sign of the horns – the "rock on" hand gesture, in emoji terms – has been common in heavy metal culture since the 1970s. It's used to express enthusiasm and gratitude for a band, and makes most people in the US and UK at least think immediately of this video. What you may not know is that directing the sign of the horns at someone in many Mediterranean and Latin countries absolutely means you are calling them a cuck.

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Cuck traditionally refers to the (often) oblivious husband of an adulterous wife, but since the US Presidential Election in 2016 it has sort of taken on a new life of its own. Now, it's better described as a term used by far-right shitposters to discredit liberals, Jeb Bush, vegans, men who respect women and pretty much anyone who criticises Donald Trump. Donald Trump, of course, being an extremely virile man with a fine head of hair and a wife who definitely doesn’t smother herself in Purell every time she has to touch his hand. Like literally everything else, cucking is also a legitimate fetish, which involves someone getting off by watching their partner fuck someone else. Start typing "cuck" into PornHub’s search bar and you will be hit with a multitude of suggested terms, each more graphic than the last. But back to etymology.

The common words for cuckolded in Italian, Greek and Spanish are cornuto, κερατάς (keratas) and cornudo – literally meaning "horned". As with most things, how offensive the charge is depends on who's on the receiving end. Spanish foreign minister Josep Pique, for instance, wasn't thrilled when then-Italian prime minister Silvio Berlusconi threw the horns behind him during a photo-op with EU leaders. Berlusconi said he was "just kidding". Franciso Almeida Leite, the political editor of a Portuguese daily paper, said, "It's a great thing to do if you want to start a fight."

In Western traditions, the sign of the horns comes from "the cuckold's horns" – a gesture in which two fingers are placed over the head of a man whose wife has been unfaithful. This is an allusion to the mating habits of stags, who forfeit their mates when they are defeated by another male. The gesture dates back to the Middle Ages and can also be seen in a load of Renaissance paintings, as well as modern political photo ops outside Downing Street. We sometimes refer to it, today, as bunny ears (although that has its own complex little history). Another variation is putting your hands each side of your head and pointing with your thumb and index fingers outstretched, like a bull.

The term cuckold itself is incredibly common in medieval folklore, literature and iconography, including a 1250 satirical poem "The Owl and the Nightingale", Shakespeare’s poetry and Geoffrey Chaucer's "The Miller’s Tale".

Janet Williams notes in a BBC article that the word derives from old French for cuckoo ("cucu") – "The females of some species of cuckoo lay their eggs in other birds' nests and leave them to bring up the offspring." This gave us the word "cuckhold", which in the Middle Ages came to mean a husband with an errant wife. "The word 'cuckold' also implies that the husband is unaware of his wife's infidelities," explains Williams. "And he might only find out on the arrival of a baby – palpably not his. Which takes us back to the cuckoo."

Of course, the sign of the horns specifically has many meanings. In Hinduism, it's known as the Apana Mudra, a yogic symbol conductive for detoxification. In Wicca, it’s used to invoke or represent the Horned God. It's similar to the gesture for "I love you" in American Sign Language. In many Mediterranean cultures, it’s a superstitious gesture for protection, sort of like knocking on wood. It is also one of the many, many things Gene Simmons has attempted to trademark – which he failed to do because it's been used for so long in so many different contexts. Simmons didn’t invent it; 13th century poets didn’t invent it; the University of Texas head cheerleader Harley Clark – who flashed the sign during a pep rally in 1955, prompting its widespread usage among Texas Longhorns fans – didn’t invent it. It's just one of those things that’s been around forever, like herpes or the wheel.