Everyone is burdened by their body in Praise. Gordon, the 1998 Australian film’s gormless protagonist, played with slack-jawed charm by Peter Fenton, is an asthmatic who can’t stop smoking; a young man chronically allergic to the way that he chooses to live his life. And then there’s his love interest, Cynthia (Sacha Horler), a barmaid who is chronically allergic to everything.

“Wool, dust, soap, beer,” she tells Gordon early on, swigging straight from a brown bottle. She covers up her eczema in thick layers of make-up and takes just-less-than-lethal doses of steroids to control it. But none of it really works.

Later, shortly after the two of them move in together, Cynthia rolls over on their damp bed and asks Gordon to scratch her scabby back. They’ve already slept together many times, not to mention talked about the possibility that they might be in love with each other. But somehow this scene is the most naked and romantic of them all. Cynthia is nervous – actually nervous, about asking Gordon to do this, which she’s never been before – and the director, John Curran, shoots the scene as if it’s the final swooning reconnection at the end of Billy Wilder’s The Apartment.

“That’s beautiful,” Cynthia wheezes after Gordon has been scratching her for a while. He gazes at her fondly.

This year Praise – based on the prize-winning novel by Andrew McGahan – celebrated two decades since its release, meaning it’s almost as old as the 25-year-old Gordon. Yet it remains unequalled in its depiction of sex; its depiction of people.

In the pantheon of classic cinematic couples, Gordon and Cynthia are all-time greats, standing out like two scabrous sore thumbs. They’re true rebels, more dangerous than Bonnie and Clyde; more thrillingly fucked-up than Titanic’s Jack and Rose; realer than Harry and Sally. They’re characters lost from the sanitised romantic comedies churned out by Hollywood today.

The first sex act we see depicted in Praise is an old, overweight man, pleasuring himself in the shower of Gordon’s apartment block. And yet because of all this grottiness, not despite it, Praise is stridently erotic. Woven through the griminess of it all – the lingering shots of sweaty bodies moving through the Brisbane summer, the sight of Gordon pissing in the sink because the lightbulbs keep getting stolen out of the apartment toilet – are real moments of naked eroticism.

Gordon doesn’t like sex before he and Cynthia meet, and Cynthia can’t get enough of it. “I’ve got this real thing for penises,” she tells him cheerfully on their first date. A lot of the sex they end up having is depicted on screen. Sometimes it’s meant to be titillating and sometimes it’s not. But all of it has this strange, beautiful romance to it.

Through Cynthia, Gordon learns that sex can be fun – that it doesn’t have to be the chore he treated it as before they met. And, through Gordon, Cynthia learns that it can be more than fun; that it can have something resembling meaning.

The effect of all this is that while watching Praise you forget that sex could ever be depicted any other way. You forget that there are other movies out there where it’s supermodels sleeping together, rather than the ordinary, intensely relatable people Gordon and Cynthia clearly are.

This, after all, is the key to the movie; the reason for its enduring power. The love story at the heart of Praise isn’t like the flashy, high-octane romance of Two Hands, released the year after Praise, or even the swooning Hollywood fairytale of Strictly Ballroom, released six years before it. This is a romantic comedy about people you actually know; people you recognise.

Another director might have been tempted to frame Cynthia and Gordon’s love story as an overcoming of the odds; a tale of two extraordinarily unloveable people somehow finding one another. But Curran’s genius lies in the fact that he doesn’t see either of them as exceptional. Cynthia and Gordon aren’t two pigeons moving through a world of peacocks. They’re not disabled, or even different, and their love, blighted by alcohol and ailments as it is, isn’t some grim joke.

Of course, their relationship can’t last, because these things rarely do. But Curran doesn’t seek to punish Gordon and Cynthia for daring to think that they might be able to fall in love. Nor, by the film’s climax, does he have them straighten out, and rise above the things that stop them from joining the ranks of high society. In the film’s oddly hopeful finale, Curran lets them be exactly who they are: two ordinary people who found in one another a beautiful, thoroughly normal, kind of love.