Never let it be said that the British Film Institute doesn’t have a sense of humour. A three-month-long comedy season starts at BFI Southbank on Monday and runs until the end of January, showcasing everything from spoofs to screwball, sitcoms to slapstick. And the BFI has got the season off to a hilarious start by playing a practical joke on its audience: it has given the 1980 workplace farce 9 to 5 an extended run, proclaiming it “a classic feminist comedy”. You guys! You kill me.

It has to be a gag, right? Anyone who has seen 9 to 5 will know that the film bears the same relationship to feminism that Jurassic Park does to palaeontology. (We could quibble with the words “classic” and “comedy”, too, but we would be here all day.) It stars Jane Fonda, Dolly Parton and Lily Tomlin as office workers who take comic revenge on their leering, chauvinistic boss (Dabney Coleman). For Fonda, who helped generate the project through her own production company, it was one of a series of films (Coming Home, The China Syndrome) in which she played a previously oblivious woman newly politicised by crisis. Her character was reset at the start of each movie so that audiences could watch her undergo the same awakening all over again in a variety of settings.

In 9 to 5, she ditched her usually earnest persona for comedy of the broadest possible kind. Pauline Kael, the mighty film critic of the New Yorker, was not impressed. She quibbled with the picture’s comic logic (“When Jane Fonda is defeated by a Xerox machine, it’s not enough that she is made to look a ninny – the Xerox machine defeats her by doing things a Xerox machine can’t do”) and its questionable shots of Parton’s body. Most of all she wondered why it betrayed its own message. Singling out the moment when Parton threatens to take a handgun and turn the boss “from a rooster to a hen with one shot”, Kael wrote: “Didn’t any of the feminists involved with this project register that a castrated rooster is a capon, not a hen, and that this joke represents the most insulting and sexist view of women?”

The cartoonish approach of 9 to 5 reduces the realities of workplace sexism and harassment to the level of the innocuous. The boss is no more than a stock Carry On buffoon, and the movie has so little faith in its premise that it makes him an embezzler as well as a creep; clearly, the film-makers don’t believe that his habit of groping and belittling female employees is sufficient on its own to qualify him as a villain. Still, it’s not quite as dodgy as the director Colin Higgins’s followup, The Best Little Whorehouse in Texas, a jolly musical that argues that prostitution is good, wholesome fun with no apparent downside. Pretty Woman looks like the SCUM Manifesto by comparison.

Thelma & Louise … it takes sex with a good-looking man to give Thelma a new lease of life Photograph: c.MGM/Everett / Rex Features

The reduction of feminism to caricature in 9 to 5 paid off at the box-office, as it has done in subsequent examples of faux-feminist cinema such as The First Wives’ Club, Fried Green Tomatoes at the Whistle Stop Cafe and Thelma & Louise. When Thelma (Geena Davis) is the victim of an attempted rape at the start of the latter, the signs are that the incident – and the murder of the assailant by Louise (Susan Sarandon) – will be handled with some sensitivity. It isn’t long, though, before the formerly downtrodden Thelma gets a new lease of life, a snazzy tousled hairdo and a career as a convenience-store bandit – and all because of an energetic evening spent with a pretty pick-up played by Brad Pitt. “When Thelma takes up with an attractive young hitchhiker … good sex has as magical an effect on her as any male chauvinist pig could wish,” observed the critic Adam Mars-Jones.

The biggest slight on the heroes of Thelma and Louise is that they are surrounded by cyphers; even the one beneficent male, a cop played by Harvey Keitel, amounts to an idealised avuncular fantasy. It’s as though the screenwriter Callie Khouri and the director Ridley Scott were worried that Thelma and Louise themselves wouldn’t be able to hack it in a film populated by complex or nuanced individuals, so they stacked the odds in their favour. How about giving Thelma a parodically chauvinistic husband who is just plain stupid into the bargain? Or a gnarly, lecherous old trucker for the women to get the better of? He could even shake his fist and call them “bitches from hell”. And what are the chances that a Rastafarian cyclist in the film will conform to his own sort of stereotype by smoking a big fat J?

Django Unchained … its black character aren’t given anything interesting to say. Photograph: Allstar/THE WEINSTEIN COMPANY/Sportsphoto Ltd./Allstar

It’s all too common for films to say one thing and mean another, and contradictions aren’t confined to the area of fraudulent feminism. Django Unchained and Three Billboards Outside Ebbing, Missouri both seem awfully agitated about racism against African Americans. Neither film, however, is quite incensed enough to bother giving their black characters anything interesting to say or do, or any real agency in the plot. No wonder it was only the white actors (Frances McDormand, Sam Rockwell and Woody Harrelson in Three Billboards, and Christoph Waltz in Django) who got the prizes and acclaim. And films with ostensibly gay subject matter often turn out to be the ones that are most squeamish about homosexuality. The Imitation Game manufactured a faux-mance between Alan Turing (Benedict Cumberbatch) and a female colleague (Keira Knightley). Philadelphia portrayed a gay couple who didn’t kiss. Jean-Marc Vallée’s C.R.A.Z.Y. was a coming-out tale that evidently wished its hero wouldn’t.

Claiming that these films oppose homophobia, or that Django and Three Billboards are straightforwardly anti-racist, or that 9 to 5 is feminist, does no one any favours. There is a deficit of diverse stories in popular culture, to be sure. But in our rush to compensate, we should be wary of celebrating the bogus article as the real deal, or mistaking a cop-out for a panacea.

9 to 5 is at BFI Southbank from 16 November.