Starring Allen Covert, Doris Roberts, and Shirley Jones. Rated 14A.

Okay, go ahead. Roll yourself a nice fat joint and take a couple of deep, committed hits. You might as well. The creators of this perfectly nitwitted stoner flick about a weed-whacked 35-year-old video-game tester forced to shack up with his grandmother and her roommates clearly sucked up healthy samples of their stash before coming up with such for-the-ages classics as a kung fu-ing chimpanzee, armpit-farting gamer geeks, and plastic-chested babes suckling said geeks.

In case it's not clear, Grandma's Boy makes no pretence of intelligence or of purpose-this willfully dumb movie is all about being crude, dumb, wasted, and dumber. Over-the-hill Xboxer Alex (Allen Covert, who looks just like a stoned Mel Gibson) is a gleefully immature underachiever at a video-game company where he's revered by a pasty pack of clichéd younger nerds. There's a sexy supervisor (Linda Cardellini) Alex crushes on and a sociopathic Matrix-manic boy genius (Joel David Moore) who threatens his spliff-happy world, plus some mentally challenged cameos by SNL alumni, but the movie and its intended audience know the only thing that's really important is reaching for the next bubbling bong. Oh, and getting elderly ladies stoned.

In a second-act set piece-not that this pot-hazed sloppy structure filled with awkward set-ups by virginal feature-film director Nicholaus Goossen has "acts", exactly-the house of Grandma Lilly (Doris Roberts) is transformed into a reefer-mad, biker-crashed karaoke party after she and the other ladies haplessly loosen up on some "funny" tea. Warning: any guy who ever had a thing for Mama Partridge will get more nastiness from Shirley Jones-whose aggressively horny Grace once gave a helping hand, so to speak, to both Charlie Chaplin and Don Knotts-than they ever bargained for. She even does a Mrs. Robinson on Jeff (guilelessly funny Nick Swardson, who cowrote the movie with Covert and Barry Wernick), Alex's man-child pal who sleeps in footie pyjamas in a car-shaped bed and refers to his parents as "my roommates".

Grandma's Boy, produced by Adam Sandler and populated by his cohorts, has nil redeeming value and pretty much no reason to exist. But there are a couple of guilty laughs that will surprise even those in a weed-free state of mind. And when that monkey gets behind the wheel of that car you'll think you've sampled the wares of every grow-op in B.C.