Jason Lee is usually the funniest guy in any Kevin Smith movie (Banky in "Chasing Amy," Azrael in "Dogma"). Julia Stiles has had fine comedic timing ever since her big splash in "10 Things I Hate About You." But they couldn't be more mismatched as romantic leads in "A Guy Thing."

A cold-feet comedy of accumulative misunderstandings about a groom-to-be who wakes up with a blonde in his bed the morning after his bachelor party -- and assumes the worst -- the movie spends most of its time mining very familiar territory. Lee hides the girl's forgotten panties, discovers she's his fiancée's cousin, and has generic nightmare run-ins with his future in-law and Stiles' ex-boyfriend.

Most of its jokes come from the compounding lies that make it hard to sympathize with the hero, and the moment you meet each one-trait character, you can see his or her entire story arc mapped out in front of you. Example: Stifled Lee, who's going to veer from his buttoned-up, conservative bride-to-be (Selma Blair) and fall in love with wild-child Stiles, has a buttoned-up, conservative brother (Thomas Lennon) who is secretly in love with Blair. Hmmm...I can't imagine where that's going.

But while I could go on and on about deficiencies in the movie's plot, the heart of the problem is that the movie has no heart because Lee has no chemistry with Stiles. Or with Blair for that matter. His innate snarkiness is perfect for the role of a beer-and-football best friend, but he has the look of a high school kid reluctantly reciting Shakespeare in front of the class when called on to be romantic, or even sincere.

Stiles convincingly smiles with stars in her eyes when her roll-with-the-punches character is called on to act as if Lee is the man of her dreams. But she might as well be acting to an empty stage. Not only is Lee a colorless chump as a romantic Everyman, but he doesn't even live up to Stiles' highly scripted generic praise of his character. "You really are a good guy, and guys like you are hard to find," she says, despite the fact that his passing out was the only reason he didn't sleep with her a week before his wedding.

Despite stock plot elements (Lee works for his intended's rich CEO father, of course) and ill-conceived subplots (Lee helps Internal Affairs catch Stiles' jealous rogue-cop stalker ex-boyfriend), "A Guy Thing" could have clicked with a more carefully chosen cast.

Keep Stiles, who holds the movie together with her fun-loving funny gal performance. Keep Blair, who is just right for the role of the too-prim fiancée. Keep the recently revitalized James Brolin as Blair's amusingly intimidating father, and keep comedian Larry Miller (from the "Nutty Professor" remakes) as the disapproving minister presiding over the last-act wedding who lingers after saying "Speak now or forever hold his peace...I'm just gonna give you another minute or so..."

But give us a lead who can seem comfortable with the refined Blair while having the charisma to be attractive to an adventurous girl like Stiles. Give us Ryan Reynolds (snarky and charming in "Van Wilder"), Jake Gyllenhaal (hilarious in "Bubble Boy"), Heath Ledger (Stiles' "10 Things" co-star) or even Josh Hartnett (who proved his comedic abilities in last year's "40 Days and 40 Nights"). Then hire Lee back again -- as the interfering best friend, a role to which he's far better suited.