Tricksters the world over agree: Middle America only exists to provide provincial types from the lower socio-economic groups for use as props by the comedy establishment. If you live in the bible belt, in fact anywhere within the red states, look out: there’s a jape-ape en route with a cameraman nesting in a hide disguised as a waste bin, ready to mine your simple intelligence for laughs. Sacha Baron Cohen, who isn’t a real baron, had a ball doing it in Borat and now here’s MTV’s Johnny Obnoxiousville posing as a randy old duffer with his obese grandson in tow, ready to wrong foot real people, whoever they may be, in a series of hilarious setups. The comedy writes itself.

Yet, watching Bad Grandpa, there’s the sense that Joe and Jacinda Public, for all their suggestible idiocy, didn’t play ball with Johnny and his entourage. Why do I say this? Well any hidden camera comedy works on the basis that the marks are oblivious to the watchers and their reactions to these taboo-busting situations are genuine. However, too often on Johnny’s road trip it’s the audience that’s been setup; half the victims unable to resist the temptation to look at the very cameras the producers have begged them to ignore; their manner too stilted, too self-aware to convince. In-credits we’re shown the reveal; the moment these unsuspecting innocents allegedly discovered they were movie stars, but clips designed to persuade us the reactions were unforced look forced, putting the matter beyond doubt.

What happened? We can’t know for sure but one suspects the team just weren’t getting what they needed from those empty headed miscreants. After all, when you’re unaware you have a part in Johnny’s movie you don’t know your lines. So perhaps they broke cover, asking for another take, suggesting a few mock-genuine reactions that would allow all concerned to hit their marks and go home. Of course they’d be a danger that the performances wouldn’t convince and that consequently the sense of artifice would kill the gag, but fuck it, the people this is aimed at aren’t likely to notice the difference, right?

That isn’t to say there aren’t funny situations in Bad Grandpa; they’re just few and far between, padded out with sub-candid camera filler. Had the setups been better, the situations more outlandish and had more unsuspecting folks not suspected it was nonsense, perhaps you’d have a movie. As it is it’s weak stuff: a flick more fun to make than to watch.

In 92 minutes I laughed twice. Once at the sight of Knoxville’s geriatric being folded on a faulty bed and once on learning that Spike Jonze was part of the brain trust responsible for the alleged screenplay; a script so intricate and layered that it appears to the naked eye as little more than a loose, postage stamp scenario upon which to hang a series of underpowered hidden camera stunts. Johnny, you got me!