On Exhibition Street, a giant toga-clad Geoffrey Rush stares out from the marquee of Her Majesty’s Theatre, an unsettling, slightly bewildered look in his eye. If you follow his gaze, you’ll end up staring directly at the Comedy Theatre, where John-Michael “Hollywood” Howson’s vanity project, More Sex Please … We’re Seniors, crawled desperately onto the stage last night.

More Sex is dead on arrival. From the first note of the MIDI backing track overture, a cloud of Dencorub-scented doom begins descending over the theatre. By the time Matt Quartermaine takes the stage in dungarees and sex-offender hair and spends five minutes playing with a vacuum cleaner, the show’s already in such dire straits you almost expect a trauma team to rush on stage carting a defibrillator.

It transpires, during the interminable opening scene, that we’re at the Guantanamo Palms Retirement Home. Yes, you read that correctly. Two couples — Myra and Roy, the uptight suburbanites, and Mac and Joan, the tree-change bogans — are moving in. There are songs. There are scenes. The jokes come fast, sometimes as many as one per line. Almost none of them land. With every passing Casio chord and synthesised crash cymbal, hope trickles away slowly, like the last drips from an IV bag.

This cast, in almost anything else, would be fine. They’re all talented comic actors. Here, they operate on a spectrum that runs the emotional gamut from bored to embarrassed. Tracy Harvey walks around like she’s badly chafed, manically over-enunciating everything as though she’s in a pantomime production of SBS’s English at Work. Michael Veitch sings half-heartedly about farts, at one point on opening night forgetting an entire verse and mumbling gibberish in tune while covering his mouth. Veitch and Harvey muck up their ode to flatulence (set to the tune of You Made Me Love You) so badly that Harvey actually apologises to the audience mid-song.

Mark Mitchell looks slightly less like he’s dying of shame than the other three leads, but perhaps it’s simply because he doesn’t care — he certainly doesn’t seem to. Jane Clifton tries hard to sell the material she’s given, but these turds weren’t even polished for a second before being thrust out on display.

Quartermaine, in a non-speaking role as the retirement home’s handyman, seems to be the scene-change entertainment. Every so often throughout the night, he lumbers out to attempt physical comedy and pratfalls to a Play School-esque faster-and-faster electric piano accompaniment. Problem is, he’s less Lucille Ball and more billiard ball.

In the program, producer Malcolm Cooke describes the show as “the first Australian musical to be written especially and very respectfully for and about seniors” and “riotously funny”. One wonders if he’s seen it. The show is patronising, sexist, racist, ageist, puerile and entirely free of narrative. But the worst crime it commits is that unforgivable theatrical sin: it is deeply and unendingly boring.

Perhaps the most bewildering aspect of More Sex is its title. The whole thing’s about as saucy as The Merry Widow; as risqué as an episode of Little House on the Prairie. For all the time spent discussing people’s nether regions — a miserable-looking, feather boa-clad Clifton is lumbered with a song about Depends; Veitch and Mitchell do an extended bit about erectile dysfunction with prop sausages — you could be forgiven for thinking seniors simply don’t have sex. These four characters hate their spouses, their children, their lives and the world. There’s not a single genuine moment of joy in the entire two-and-a-half-hour ordeal.

Of particular, horrifying note is the extended audience participation section, where Howson has rewritten the lyrics to the Hokey Pokey as a threatening paean to prostate exams. It’s worth noting that less than a third of the audience deigned to involve themselves as a rubber glove-clad Clifton and Harvey desperately feigned enthusiasm in nurse outfits.

The whole thing is helmed by former actor and current amateur musical theatre director Pip Mushin, who has enthusiastically assigned people places to sit and stand. Adam Gardnir’s immovable set and ho-hum costumes are flat and unimaginative. Lighting by Nick Higgins is boring; even the follow-spot operator seemed embarrassed to be there.

John-Michael “Master of the Single Entendre” Howson’s execrable book pulls off the extraordinary feat of being even worse than his book for Dusty: The Original Pop Diva. Peppered with bizarre cultural references, Howson’s show seems to exist in a world where Les Girls is still playing Kings Cross, Murder, She Wrote and Blue Heelers are still on television and Paris Hilton is still noteworthy. Somehow, in his addled head, it’s 1972, 1995 and 2006 all at once. At one point, the jokes get so thin on the ground that Mitchell’s character delivers a short “Vegetarians! They’re a funny bunch of weirdos!” speech. Peter Sullivan and Mike Brady’s original music is tuneless, repetitive and insipid, and the only thing worse than the tunes are Howson’s abysmal lyrics (“Life is full of apple pie / No need to sob and sigh / Not ready to die”).

As the adage goes, things are funny because they’re true. Howson’s gotten a little confused, convincing himself that if something’s true it must also be funny.

Spare yourself this broken-down shuttle-bus of poo jokes, Indian call centre jibes and sexual-assault-is-hilarious gags. Go across the road and see Geoffrey Rush instead.

The details: More Sex Please … We’re Seniors plays the Comedy Theatre until December 9, with a national tour to follow. Tickets via Ticketmaster.