Anyone who puts down Hot Tub Time Machine (MGM/UA, 3.26) as…whatever, unfunny or not funny enough or insubstantial or that it’s only for 35-and-overs is at least somewhat clueless. Or dead inside. I just came out of a HTTM screening at the AMC 34th Street, and this ridiculous/gimme-a-break/hellzapoppin’/gross/outrageous/brilliant time-space-continuum comedy played like a friggin’ riot. Well, as a very clever and funny piece for the first two-thirds and then like a riot during the last third — how’s that?

It’s Back to The Future with vomit and madness and Crispin Glover absurdity and nostalgic ’80s satire, and even a guy pretending to be Biff, that pudgy, obnoxious, one-expression dickhead in all three Back to the Future flicks. It’s Groundhog Day with black-guy semen splattered over its face. Well, not really semen but facial soap that looks like it. The “movies”, you know.

Hot Tub Time Machine is complete bullshit and sloppy as hell, but it takes you on an inventive, anarchic and clever-ass ride that makes you laugh, and then laugh more loudly, and then say to yourself, “Is this really happening? Is a straight guy really being forced to blow his straight friend in front of a crowd of hooting maniacs?”

The director is Steve Pink — heretofore to be recognized as the kind of sick madman that Hollywood youth comedies need and must have. The screenwriters are Josh Heald, Sean Anders and John Morris, working from a story by Heald.

God bless the sensibility of producer-star John Cusack for bringing this truly sick, in-and-out hilarious and philosophically reprehensible comedy to the big screen. Cusack is a hoot in this thing, as you might expect, but the real breakout is Rob Corddry, who plays the wild-card wildass in the group of four (Cusack, Corddry, Craig Robinson, Clark Duke ) who visit a broken down ski resort and travel back to their youth in the mid ’80s and…don’t ask.

It’s all too crazy and sick to recount, but it has a philosophical point, which is that your fate and your future are not set in stone, and that you only have to man up, throw the dice and change what you don’t like.

Everyone behind and in front of the camera was almost certainly on mescaline when it was written and made, and I know that I have to see it again soon, and at a theatre that doesn’t muffle the fucking sound like those ayeholes at the AMC 34th Street did tonight.

Will Hot Tub Time Machine make as much money as The Hangover? Maybe, maybe not…but I know one thing — this movie is smart and nuts and anarchic in a way that redefines the term. It’s my idea of what truly insane, throw-it-out-the-window, fuck-all smartass comedy should ideally be and feel like.

It’s better than The Hangover — funnier, sicker, more insane but also with a much trippier and crazier script. It looks like some grubby New Line comedy from 1992, but the pace is relentless and it gets funnier and funnier and funnier. Stupidly, okay, but accelerated with a seriously brainy bent.

The people saying that Hot Tub Time Machine was made especially for Gen-Xers and others who remember the ’80s are…okay, maybe half-right. But any age group should (and I think will) be able to recognize true batshit insanity when they see it.