They say great comedy comes from extreme pain and, in the case of There's Something About Mary, the more excruciating, the better. Whether it's a fish hook stabbed between the teeth or a gnarled penis crushed in a trouser zipper, the Farrellys' maxim isn't so much make 'em laugh as make 'em squirm.
In the hands of lesser directors, the basic plot mechanics would make for a pleasant, if inoffensive, rom-com. But rendered pop-eyed and gasping in the choking grip of the Dumb&Dumber duo, the light tale takes second place to five set-pieces that mercilessly hammer the funny bone to breaking point.
First up is the bit with the zipper. Then there's the bit with the fish hook, two bits with a drugged-up dog (one with tranquillisers, the other with speed) and a hair-gel/semen mix-up that will have you retching in your popcorn. No joke is too base, no target too easy, as one-by-one a whole herd of sacred cows are nudged into the abattoir: homosexuals, cripples and the mentally disabled are all mercilessly hacked at. It makes for a curious combination of sappy romance and gross-out slapstick, coming on like the bastard offspring of John Walters and The Three Stooges.
As the Miss Right stalked by a slathering mob of Mr Wrongs, Diaz mixes tomboy charm with sex-bomb spunk and proves a surprisingly good sport throughout. (How many Hollywood actresses do you know who would willingly smear semen into their hair for the sake of a juddering belly laugh?)
But it's Dillon who's the real surprise here. Sporting a pencil-thin sex-offender moustache and top lip curling under the weight of his cartoon tombstone teeth, his double-dealing detective is a revolting creation. Like Jeff Daniels in Dumb&Dumber, he reveals a previously untapped talent for comedy.
The epitome of greasy villainy, every time he slimes on screen or, worse still, rubs close to Mary, you're rendered paralytic with cringes. He also spews some of the best lines (there's an indecent guffaw to be had when he describes a mentally-challenged friend called Mongo as having "a forehead the size of drive-in movie theatre").
That's not to say there aren't problems. Latex-faced comedian Lee Evans is wasted as Dillon's stooge, struggling with an American accent placed somewhere between Croydon and Carolina. He's rationed just one routine - an excruciating sequence involving car keys and crutches - as a showcase for his bendy-limb brand of comedy. It's clear, too, that the scatter-shot script has had its own crutches kicked away from it by the hour-and-a-half mark. Come the third act, it's left dawdling around a slew of sub-plots and flat gags, killing time until an inevitable, unsatisfying finale that fidgets between low-brow farce and high-gloss feelgood.
It would be tighter and funnier if the excess flab was cut from the script. But, like seemingly every other Hollywood release this year, There's Something About Mary falls victim to the 20-Minutes-Too-Long syndrome. The redundant Jonathan Richman as a guitar-strumming Greek chorus is a self-indulgence we could have all done without.
While five revolting set-pieces do not a great comedy make, there's enough belly-croaking gags to make it a cackle-friendly trip to the flicks. Be offended. Be very offended. And then laugh your mouth off at the filthiest, funniest movie of the summer.