Screening a preview for a mixed audience that includes members of Gen Y is the acid test essential for a comedy, especially in this over-exploited genre.

And it worked. The unstoppable James Cussin’ Franco made it work. Despite all the easy shots, despite some poor overseas reviews, we lapped up Why Him? from the moment he strutted onto the screen trailing profanities.

I, for one, was not ready to be charmed by Franco or this film, in which he plays vulgar Silicon Valley billionaire Laird, who is planning to propose to his student girlfriend Stephanie (Zoey Deutch) – to the horror of her visiting parents, Ned (Bryan Cranston) and Barb (Megan Mullally).

I was readying accusations of misandry for Cranston’s insulting depiction of 55-year-old Ned but, what the cuss – it’s just so cussing funny. A full theatre doesn’t lie – we cringed on cue but we laughed far more often, and often at ourselves, or who we were, or who we feared turning into.

Against incredible odds there is heart in this film, of the not-unfamiliar father/daughter ilk.

And despite Cranston’s facial contortions during scenes involving everything from a Japanese bidet to awkward sex to exploding moose, the tiny core of mutual care embedded in adversaries Ned and Laird, along with the star-crossed chemistry between Laird and Stephanie, keeps one small edge of this crazy vehicle on the road.

The coming-of-age, father/son arc of Ned and 15-year-old Scotty (a terrific Griffin Gluck) and the antics of Keegan-Michael Key as Laird’s manservant Gustave are a bonus.

Some may self-righteously pity Cranston’s “fall” from the heights of Breaking Bad but you can see he enjoyed himself. The one left a little behind in the chaos is Mullally, the long-suffering, straight-up wife, but hers is a genuine and well-founded fear of chaos, and she does get to play that old “Mum does dope” joke.

Yes, it doesn’t take long for the bones to show through: a little Father of the Bride, that Baby Boomer vs Gen X thing, a decent splash of writer/director John Hamburg’s previous Fockers franchise and a sprinkle of Farrelly brothers excreta, but it really doesn’t matter – in the end the piss is taken out of everyone, including Middle America, California, stereotypes of every age, sex and income, even Elon Musk, thank cuss.

Throw in an acknowledged tilt at the Pink Panther movies (misinterpreted by many US critics) and it’s clear that, hey, we’re watching a circus here (including the animals) so just sit back, drop the politics, shut the cuss up and enjoy its surprisingly affecting core.

You were fairly warned by Hamburg’s previous work and/or the trailer. The Oscar-aimed, meaningful historical movie is in the cinema next door. In here it’s Why Him? – a cussing riot and great holiday fun.

Trailer warning: Contains strong language

Why Him? opens in cinemas on Boxing Day.