Jason Lee, looking so sheepish he's practically ready for shearing, sits in the middle of his bachelor party at a raucous bar, having no fun at all. "A Guy Thing" is only two minutes old, but we've already learned plenty, most notably that Paul (Lee) is engaged to the perfect Karen, but his eyes droop just a bit when she's mentioned, like she's homework that he hasn't finished. Then, when Julia Stiles shimmies into the bar in a bikini top and hula skirt — she's a semi-exotic dancer hired for the occasion — Paul perks up and offers her a beer. Hmm, where can this be going? And what will Karen think, when she arrives at Paul's apartment the next morning and finds the hula girl there?

"A Guy Thing" gamely trots through the paces of its story: Boy meets girl, boy already has other girl, boy hides first girl's underwear from second girl ... oh, never mind, you can figure it out yourself. Suffice to say that poor perfect Karen is doomed to join cinema's list of roadkill fiancées (actually, the fact that she's played by Selma Blair, who's making a career out of playing the Preppy Girl in a Turtleneck Who Doesn't Get the Guy, is a bit of a tip-off), that Lee and Stiles are cute as a button together, and that the movie has a couple of genuine laughs. (The best one is a play on the movie's title, spoken by an understanding clerk.)

Stiles, surprisingly, is the revelation here — this seems an awfully lightweight vehicle in which to unleash a star turn, but she's got a genuine sparkle, minus the too-cool-for-school boredom she's been known to exude. Her character, Becky, isn't given much personality by the written-by-committee screenplay (other than a tendency toward clumsiness); Stiles gives her a wry, self-deprecating humor and airy sweetness, and the always-likable Lee is a good match for her.

In the hands of a more skilled director (Chris Koch is best known for "Snow Day") and a better screenplay, this one could have been a charmer, but "A Guy Thing" gets bogged down by predictable supporting characters and some tasteless humor. (Since when did a diarrhea scene become a staple of romantic comedy? Is it some sort of weird bonding ritual? Hugh Grant and Sandra Bullock had a similar scene in "Two Weeks Notice," and they couldn't pull it off either.)

Add to this Becky's psychotic ex-boyfriend, Karen's snobbish parents, Paul's polyester-clad mom and stepdad, an alcoholic aunt who likes to grab men's crotches, the disapproving minister next door, a would-be caterer with a taste for pharmaceuticals, and Paul's best buddy/sidekick, who likes to refer to himself in the third person ("Jim is on it!"). "A Guy Thing" is a very busy movie about very little. The Space Needle and Pike Place Market turn up fleetingly; the film is supposedly set in Seattle but filmed in Vancouver, B.C. For a local audience, it adds just another level of disorientation to a movie that never quite finds its focus.

Moira Macdonald: 206-464-2725 or mmacdonald@seattletimes.com.