20th Century Fox Jack (Ashton Kutcher) and Joy (Cameron Diaz) enjoy their Vegas wedding, then later, sober, must face the aftermath.

There are outrageous and endearing Cameron Diaz romantic comedies, such as "There's Something About Mary," and there are middling and forgettable ones, such as "What Happens in Vegas."

Through both varieties, Diaz brings her sunny, sassy persona to the screen in ways that make her fans happy. This is a woman who can make a crack about Ashton Kutcher pouring popcorn down his pants and emerge relatively unscathed, even when she's asked to apply an anatomical term to the experience. It's called rising above your material, and not everyone can pull it off.

Diaz is a skilled physical comedian who knows how to flop on the floor with the best of them. She's got a nice sense of comic timing and knows how to deliver a punch line. She's game for just about anything (as those who remember her antics with hair gel will recall) and is willing to sacrifice any semblance of personal dignity if it will make her audience laugh.

The problem is that Diaz needs at least a halfway decent script and director to make a film that you won't forget by the time you're to the parking lot.

In "What Happens in Vegas," Diaz gets an obliging partner in crime with Kutcher, who is a nice match for her dizzying on-screen silliness. His Jack is an underachieving New York sexpot who manages to get fired by his own father (Treat Williams) from the family business. Her character, Joy, is an uptight Wall Street type who gets dumped by her fiance because of her fussiness.

Both head to Vegas to nurse their respective wounds, bump into each other, indulge together in a wild night of carousing and wind up married the next morning. (When Joy asks her best friend and travel companion why she didn't intervene in the wedding, the hung-over creature replies, "Seriously, I like threw up in my own purse.")

Director Tom Vaughan manages to keep things relatively buoyant while the film operates in more of an acerbic black-comedy mode. Forced by a vindictive judge (Dennis Miller) to live together for six months before they can divorce, Jack and Joy snipe at each other and reach predictably outrageous heights. (Be warned: In a scene that adds to a current movie trend, Kutcher pays an on-camera visit to "Urinetown," and we aren't talking about the Broadway musical.)

As the inevitable sparring best-friend sidekicks, Rob Corddry and Lake Bell jab at each other with proficient glee. But the awful moment has to come. You know the incredible sinking feeling: when the music starts to shift toward the sentimental and the dialogue gets sweet and goopy.

When the formula love story finally kicks in, any sharpness and originality promised by the film in its earlier stages gets pounded into a mushy pulp. Yes, it happened in "Vegas," and it's too bad it couldn't have stayed there.

— Distributed by McClatchy-Tribune Information Services.