It's hard to imagine that a film celebrating sex could make you want to rip out your own genitals, but such is the magic of A Dirty Shame, John Waters' tedious, repetitive, groaningly unfunny comedy about a housewife named Sylvia Stickles (Tracey Ullman) who becomes a sex addict after bonking her head in a traffic accident.

Sylvia meets a sex guru (a tired looking Johnny Knoxville) at the scene of the accident who goes down on her newly "burning bush" and tells her she's been chosen to deliver a new sex act to the world.

Some of Sylvia's neighbours form a decency brigade, spouting moronic one-liners such as "I'm Viagravated and I'm not going to take it any more!" The rest of the people in Baltimore come forward to reveal their allegedly wacky sex fetishes one by one, in vignettes that are more likely to turn your stomach than turn you on.

Call me hypersensitive, but an elderly policeman who gets off wearing diapers -- in one instance while breaking into a home to find an actual infant -- is too close to pedophilia for comfort. The same goes for Sylvia's daughter (Selma Blair), a stripper with monstrous, fake boobs who says she developed her own sex addiction at age 11. If Waters wants to go around offending people, that's fine. But making jokes involving children is creepy.

Mostly, Waters offends by being boring. His idea of a great plot twist is to have Sylvia bonk her head and turn frigid again. His idea of clever casting is to give the best lines to Patty Hearst (who still can't act, even after seven films) while letting genuine talent like Chris Isaak twiddle his thumbs as Sylvia's husband.