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You can picture the script meeting: how to get everyone in the key cinemagoing demographic, from 15 right up to 40, laughing at the same movie? Could the thirtysomething concerns of Seth Rogen’s ‘Fret’ Pack oeuvre be merged with the carefree, keg-party shenanigans of the frat-com? Dare they try?

Called Neighbors in the States, where the words Ramsay Street mean nothing, the resulting pitch must have had the execs salivating. Effectively it’s Knocked Up meets School Of Hard Knockers , no matter that the latter is actually a spoof movie as seen on The Simpsons . It’s a risky little gambit, but one pulled off with surprising frequency. No sniggering at the back.

We first meet suburbanites Mac (Rogen) and Kelly (Rose Byrne) in the middle of unlikely tops-on sex. “I’m taking you to the Bordertown, bitch,” trash-talks Mac without conviction. “Don’t call me bitch!” she complains, with a fair bit more. But there’s a reason it’s all so stilted: their baby, Stella, is watching.

“She only sees shapes,” assures Kelly. “Shapes fucking each other!” is Mac’s exasperated answer. The scenes that follow offer a witty, convincing portrait of young, grin-and-bear-it parenthood, engagingly played by Rogen and Byrne (rocking her own Aussie accent for once).

Then, as if summoned by the great movie genie, Teddy (Zac Efron), Pete (Dave Franco) and their party-hearty Delta Psi fraternity take up residence next door. One night Mac and Kelly go round to complain about the noise, but end up joining in the mushroom-spiked hedonism. Mac and Teddy get bonged up and have a Batman-off (Keaton vs Bale).

Kelly asks Teddy’s girlfriend Brooke (Halston Sage) how they first met. “I saw him, he saw me,” is the blithe response. With the stage set for all sorts of age-gap comedy goodness, director Nicholas Stoller ( The Five-Year Engagement ) and writers Andrew Cohen and Brendan O’Brien steer the film straight to montage mode.

“They won’t stop partying!” complain Mac and Kelly in pretty much the following scene, starting an – immediate – almighty feud. One moment Mac floods their basement with water, the next the boys are sculpting dildos for sale to cover the damages. Two minutes later: “Holy shit guys, I think we made $10,000!”

While the frathouse scenes could use more room to breathe, and the concertina-ed timeline sometimes strains, Efron is smartly cast as the smiling Delta psy-chopath-in-waiting, while Franco wrings lots of laughs from his sidekick role. McLovin (aka Christopher Mintz-Plasse) and Submarine ’s Craig Roberts are in the mix, too, but get lost in the whirlwind.

At least there’s a sound reason for those strawpedo-ed (Google it!) plot points – to speed us to the next set-piece. And Stoller serves up some corkers, from throwaway visual gags (Rogen and Byrne grappling with a suggestively topiaried bush), to fiendishly involved ones (Rogen playing find-the-airbag). The sequence featuring a hungover, heavily lactating Kelly brings the house down – and might do the same to the Mumsnet server.

In truth, there’s quite a bit more here for “bros” than “hos”, to use the film’s troubling lingo. Kelly and Lisa Kudrow’s angry dean are pretty much the only female characters with any agency/clothes. There’s a near-the-knuckle rape joke. And little Stella is variously threatened or forgotten, then made to dress up as male TV characters such as Don Draper and Walter White. “Let’s get all the leading men out the way!” says Kelly, ignoring a century of female icons. It’s not hard to spot that someone has a few gender issues here – most likely Hollywood itself.

The get-out-of-jail-free card throughout is that Bad Neighbours is consistently, sometimes epically, funny. Rogen has some great, seemingly improvised, lines: referring to Efron’s terrifying abs as “a great big arrow pointing towards your dick” and describing intercourse with an embarrassed, vest-wearing Kelly as “like having sex with Tony Soprano”.

Franco, meanwhile, is the proud possessor of an extraordinary stiffy, and not afraid to use it. Well, maybe a bit. “It’s a blessing and a curse!” he wails in swollen agony/ecstasy, nearly hobbling off with the entire movie. You never forget you’re watching a well-oiled machine, often an extremely well-oiled one, but Bad Neighbours is front-loaded with charm, and there’s lots of filthy fun to be had as it whizzes past.

It’s a rare comedy that’s more remarkable when it’s chilling than when it’s going crazy, but that’s arguably the case here – although the chances are anyone in the lower half of club 15-40 might not see it that way.