A slob farce with about a six-pack of lowbrow highlights and a whole case of empties, There's Something About Mary stars Ben Stiller as a mopey would-be writer who's obsessed with finding the girl who left him on prom night 13 years before. To that end, he hires a sleazy private eye--Matt Dillon with a porn-star mustache--who promptly tells him his Mary's now obese and bedridden, with several kids by as many different fathers. As Stiller discovers, however, Mary is actually lithe, wealthy Cameron Diaz, and Dillon is using all his research to worm his own way into her good graces.

The directors, Peter and Bobby Farrelly--the brain trust behind the spotty Dumb and Dumber and the execrable Kingpin--score some cathartic belly laughs on effrontery alone. Their talent is for gross-out sex gags and hyperbolic cruelty, and as long as they stick to defibrillating drugged-out dogs and swapping jism for hair gel, they really know how to tickle your inner 13-year-old. But the constant retard jokes and gags about cripples are irredeemably sour--especially combined with the Farrellys' grotesque sentimentality. It's awful to wring yuks out of Mary's brother's mental condition; it's worse to make him a lovable pet, so that the audience says, "Aw, bless his heart," every time he appears.

In interviews, the Farrellys take the obvious dodge that they're sending up "political correctness" by ridiculing people in wheelchairs or people with mental disabilities. That wouldn't be the first time somebody confused political correctness with common decency. The reason the gags don't work, though, isn't some self-righteous liberalism on the audience's part; it's that mockery is a weapon, a leveler, and only a creep would use it against underdogs of any stripe. Here, as in the snarky, coldly calculated The Opposite of Sex, no zinger is too risible as long as it's delivered by an unlikable character: That way nobody can accuse the filmmakers of being bullies (or homophobes, or racists), but they can still get their cheap laughs. That also effectively makes the movie's critics seem uptight, which may explain the hysterical overpraise that There's Something About Mary is getting--including marks for the Farrellys' "bravery."

As filmmaking, There's Something About Mary is so dull and functional it could've been shot by surveillance cameras: The directors' idea of staging a conversation is ping-ponging back and forth between talking heads. (Their major influence must've been Atari.) The ramshackle staging sometimes leaves you unsure even how to respond, as in a poorly constructed subplot involving a suitor in leg braces (that amazing clown Lee Evans).

But better moviemaking might only have dampened the explosive crudeness of the gags that work. And give the Farrellys credit for two very astute casting choices. Well on his way to becoming the funniest straight man in movie history, Ben Stiller makes a brilliant shtick of thwarted politeness: To me, he gets the movie's biggest laughs trying to make small talk with a hitchhiker who's plainly a few beans shy of a burrito. And as a running musical chorus, like Nat King Cole in Cat Ballou, that rockin' leprechaun Jonathan Richman sounds a welcome note of sweet, innocent mischief every time he appears. Maybe that's because you wouldn't hear Jonathan Richman making retard jokes.