Two marriages turn up in Cameron Diaz’s new comedy; one of them involves a ceremony that ends unfinished, while the other apparently takes. The marriage that doesn’t work at all, unfortunately, is the attempt by writer Nancy M. Pimental to wed the Cute and the Smutty in her script for the movie. The combination that results (call it either Smute or Cutty) is supposed to amount to “The Sweetest Thing,” but it’s far from it.

The picture, which has a lot to do with female camaraderie (a hot topic right now, with “Sex and the City” on HBO, and “Crush” and now this on the big screen), centers on Christina (Diaz), a blonde San Francisco bombshell who’s notorious for captivating guys and then unceremoniously dumping them. By chance, however, she bumps into the perfect fellow in a bar one night: he’s Peter (Thomas Jane), a flaxen-haired piece of beefcake with a winning smile. You can tell immediately that they’re destined to fall for one another, since they initially exchange nasty, dismissive remarks. (It’s the old scripter’s ploy, which might be described as Love at First Slight.) But the next morning Peter has left for his home town, a little place upstate called Auburn, where–Christina believes–he’s serving as best man in the wedding of his obnoxious brother Roger (an almost unrecognizable Jason Bateman). Under prodding from her sharp- tongued buddy Courtney (Christina Applegate, with dark hair that makes her look almost like Jennifer Aniston and–as one brutally overextended comic scene emphasizes, highly padded boobs), our heroine decides to travel to Auburn and tell Peter how she feels about him.

At this point “The Sweetest Thing” turns into a girlie road movie in which Christina and Courtney share a series of wacky adventures along the way–much like Romy and Michele (though considerably less funny); many of them, drooling young males will be happy to know, involve the two stripping repeatedly down to their undies and jiggling their behinds. Eventually they get to the wedding, but what they find there isn’t quite what they expected, and it takes a number of false starts and stops before Christina and Peter decide what those of us in the audience have perceived from reel one–that they’re destined to be together.

As is made clear from an initial montage of guys whom Christina has loved and left over the years, what the movie is about–surprise, surprise!–is an inability to commit; but the threadbare contrivance of a luscious girl chasing a handsome guy to do precisely that, with its myriad attendant complications, proves a frail skeleton on which to hang a full-length feature. That explains why Pimental has added so much tangential matter to get the narrative up to a meager eighty minutes. (With some unfunny out-takes added over the closing crawls, too, the picture seems as padded as Courtney’s breasts.) We not only have the road trip stuff, complete with a visit to an awful dress shop run by Georgia Engel, the spacey dingbat who played Ted Baxter’s wife on the old Mary Tyler Moore show (hi, Gloria!), but lots of other random bits, too (one involving a lascivious biker, another a nervous would-be bride, a third the two girls’ shy friend plain Jane–played by Selma Blair–who gets it on with a fellow who dresses in animal costumes to entertain kids–no, his name isn’t Smoochy). Entirely too large a percentage of the jokes involve sniggering sexual smarminess: one has to do with one woman apparently servicing another in a speeding car (to the glee of an onlooker), another with a woman getting stuck most uncomfortably while giving her man oral sex. Another episode, in which Applegate struggles to relieve herself in a male’s urinal, isn’t sexual but is pretty disgusting. The structure of the picture is frankly a mess: it seems to have been written, shot and cut with a series of pop tunes in mind, which are inserted at key points to “comment” on the action we’ve just seen. (In the instance of the oral sex gag, the script drags in a rendition of Frankie Goes to Hollywood’s “Relax,” perhaps the ’80s tune most signally overused in recent movies. If he were alive, Holly Johnson would be reveling in the royalties.) At one point, Courtney asks Christina, “Do we have time for a movie montage?” (wink, wink) and for a few minutes the two don different outfits and preen ostentatiously for us. (This sequence might have worked except for the fact that looks totally ad-libbed–and ineptly so.)

One could go on almost indefinitely about the shortcomings of “The Sweetest Thing,” but ultimately it can simply be dismissed as little more than a big-screen version of “Sex” or “Friends” with an additional quotient of suggestive raunchiness. Despite the low quality of the material and the apparent encouragement of director Roger Kumble to mug the living daylights out of every line and situation, however, the performers manage to remain fairly ingratiating throughout. Diaz may overdo the ditzy blonde bit, but she has a winning smile and maintains an air of innocence even at the most vulgar moments; she also demonstrates solid comic timing. Jane is a likable hunk, Applegate does the catty best-friend bit with aplomb, Blair is convincingly mousy, and Parker Posey gets by with some old shtick involving a bride’s natural nervousness. But their talents all seem misapplied to a picture which, despite its title, seems at heart a sour, misanthropic mixture of sexual grossness and slapstick.