They sign up for pick’n’mix and free films, but have to deal with rutting teenagers, rotting food and cups of excrement. Who knew the movies were so gross?

Cinema’s real superheroes are not the vigilantes in Lycra who caper around on the big screens, but the underpaid employees stalking the aisles armed only with popcorn sweepers. Each season presents ushers with distinct challenges. At Christmas, parents use cinemas as a creche as they go present-shopping; come spring, they let their Easter-egg-stuffed offspring vomit in the cup holders; but the six-week summer holiday stretch is the most intense, when a combination of boredom and blockbusters turns everyone feral.

A decade ago, I was part of a teenage cohort working for minimum wage at a small cinema in Cornwall. I learned many valuable lessons, such as how to answer the question: “What do you mean: ‘It’s sold out?’” with no trace of sarcasm. I learned about the toxic powder that could turn liquid sick into a scoopable solid. I discovered that humanity was even richer than the green (The Incredible Hulk), moneyed (Sex and the City) and melodramatic (Mamma Mia!) tapestry on screen. There were ways of making life easier, such as reminding tourists used to chain multiplexes that our films actually started at the time advertised. Telling sweet old ladies where a period drama was set meant they didn’t wait until the end of the credits to find out, thus hastening their exit and allowing us to clean up sooner. Not that fans of The Duchess made much mess compared with the Iron Man aficionados.

‘I was part of a teenage cohort working for minimum wage at a small cinema in Cornwall’ ... Laura Snapes in her usher days. Photograph: Laura Snapes

Other behavioural oddities were less preventable: as well as “sold out”, “reserved seating” was apparently a difficult concept to grasp. Like most cinemas, we turned a blind eye to food brought in from outside. But we had to enforce a specific ban on pasties, which aren’t only messy, but also smell uncannily like BO. This made asking customers whether they were smuggling in a large Rowe’s steak pasty an awkward conversation – maybe they just had poor hygiene. I once found an empty seafood platter under a seat and felt for the neighbour of whoever sat there slurping down whelks like wet, fishy popcorn. On witnessing a blowjob in progress in the back row, I sprinted down the hallway to ask the manager what to do. “Stop them, obviously!” I legged it back: it was all over. Never had I been so grateful for the speedy satisfaction of teenage boys.

But after speaking to a crop of current and former ushers, I think we got off lightly. One employee of a Hertfordshire cinema shudders to recall a recent “week of bodily fluids” that left staff capable of identifying a comprehensive range of effluents at a glance. Gary from Manchester explains that the ushers would often consume the sweets that customers left behind, but never the drinks. “Not after the time we found that someone had left behind a hot wee in one Pepsi cup and a steaming shit in another. Was Transformers: Dark of the Moon so interesting that they couldn’t have left to go to the toilet?”

You sign up for a cinema summer job envisaging free films and pockets stuffed with stolen pick’n’mix, not, as a distressing amount of ushers lament, confronting cinemagoers’ desire to poo anywhere but the toilets. As if bringing a baby to the cinema weren’t antisocial enough, some parents change their nappies in a screen. “As I was hurriedly collecting filth for minimum wage, my foot knocked against something weighty under a seat,” says Rory, also from Manchester. “I reached under, picked it up and held it up to the light. I realised I was holding a used, full nappy. I can confirm that we provided baby-changing facilities.” The environmental catastrophe that Dwayne “The Rock” Johnson tackles in San Andreas pales in comparison with the used sanitary towel that Holly from Letchworth Garden City found after a screening of the 2015 disaster movie.

Facebook Twitter Pinterest ‘A lot of couples don’t even have the shame to hide that the film is irrelevant – just “Two for whatever’s on next.”’ Photograph: Getty Images/iStockphoto

People have been misbehaving at the cinema for as long as cinemas have existed. Patrons of the silent film era had to be reminded to remove large hats and were asked not to whistle. “We’re not observable in the dark, so we feel less inhibited in a variety of different ways,” says Cary Cooper, a specialist in organisational psychology. “You think you can get away with totally inappropriate behaviour that you wouldn’t do if it was light.” It is worse in “island cultures” such as Britain, he says, where we are “more inhibited to confront people about their breaking of the norms”.

Every week, listeners write in to Mark Kermode and Simon Mayo’s BBC Radio 5 Live Film Review to complain about cinemagoers contravening the code of conduct that the pair created in 2010. (“No rustling”, “no slurping”, “no shoe removal”, etc.) “I think it was probably linked to the explosion in mobile phone use,” says Mayo. “I’ve been in films where people have been taking photographs of the crowd – with flash – during the film. All these kinds of things wouldn’t have been possible or thought of a few years ago. It’s the digital revolution that has changed everything and I think that’s the fuel behind the rage we tap into every week.”

We found that someone had left behind a hot wee in one Pepsi cup and a steaming poo in another Gary from Manchester

Mayo wonders whether cuts in cinema staffing have led to a rise in unchecked bad behaviour. “The very thought of an usher coming in and telling people to be quiet or put their phone away – it would be incomprehensible.” The code is intended as a stand against slipping standards, even though he knows that most of the show’s listeners conform to Cooper’s bystander effect, seething silently rather than confronting offenders.

One type of cinema delinquency has a more complex social history than simply chucking popcorn around. “Just as the cinema generated new opportunities for working-class courtship, so did it have a similar impact on queer culture,” writes Matt Houlbrook in Queer London: Perils and Pleasures of the Sexual Metropolis, 1918-1957. When homosexuality was illegal in Britain, many gay men held clandestine assignations in cinemas. “Indoors yet public, commercial yet open, music halls and cinemas sustained a sexual culture unlike anywhere else,” writes Houlbrook. “None of the outdoor locations where men found sex were as safe. In none were the sexual opportunities as concentrated.”

Wishing to escape parental scrutiny but lacking the cash for hotels, teenagers also made a sexual sanctuary of the cinema. “Mothers of America / let your kids go to the movies!” Frank O’Hara wrote in his poem Ave Maria. “They may even be grateful to you / for their first sexual experience / which only cost you a quarter / and didn’t upset the peaceful home.”

Facebook Twitter Pinterest ‘I’ve been in films where people have been taking photographs of the crowd – with flash – during the film’ ... Simon Mayo of 5 Live’s Film Review. Photograph: Flashpop/Getty Images

Perhaps today’s back-row fumblings are tributes to these noble histories. But let’s be honest: they are mostly exhibitionism. “It’s unbelievable how much it happens – genuinely almost a daily occurrence,” says Jane in Manchester. “A lot of couples don’t even have the shame to hide that the film is irrelevant – just ‘Two for whatever’s on next.’” Mayo claims that the show hardly receives any complaints of that nature, but he admits that their producer may filter them out. “The bulk of people who have sex in the cinema, it’s because they’re not going to get caught,” says Cooper. “For others, [the idea of getting caught] will be a thrill.”

A chilling number of ushers mention finding sex toys – some still packaged, some not. Knickers and used condoms are regularly left among the popcorn crumbs. One usher recalls a colleague finding a bloodied teenage girl in the toilets. “She was physically OK, although maybe emotionally and mentally scarred.” Rough sex in the seats had caused her partner’s foreskin to tear. “He was, reasonably so, panicking. When we said we had to call the ambulance and even their parents, they freaked out even more. Turns out they weren’t dating – he was her boyfriend’s best mate.”

One way of tackling cinematic misdemeanours, says Cooper, would be to turn up the lights a bit. But where would be the fun in that? It is possible that highlighting the poor ushers left to pick up your popcorn (or pants) might deter patrons from acting up, he says, citing the success of similar safety campaigns on motorways. “It does inhibit that behaviour when you make it human.”

So, this summer, try your best not to subject the underpaid ushers to horrors beyond having to watch Hotel Transylvania 3 eight times a day. Arrive on time, put your mess in the bin and, for God’s sake, use the toilets.