A few years down the road, will the title “What Happens in Vegas …” confuse those few who come across it while rummaging in the bargain DVD bin? Such is the risk involved in taking the title of your feature film from a chamber of commerce advertising campaign — albeit one that’s become a pop-culture cliché.

Judging from the slovenly way this most unromantic comedy has been shot, edited and written, however, those responsible were not very concerned about how the movie will be received five weeks from now, when it will already be a dim memory, let alone five years hence.

Only the principal players emerge from this exercise in cinematic negligence unscathed. This is not to say that as a pair of mismatched lovers Cameron Diaz and Ashton Kutcher exactly cover themselves in glory. But their pluck and irrepressible high spirits win a measure of sympathy from the audience, if only because almost everyone who works for a living can appreciate what it takes to keep smiling through even the most pointless of tasks.

The premise of “What Happens in Vegas …” is as old as theater itself: A man and a woman with nothing in common are compelled into close quarters, as if to challenge the maxim that love finally will conquer all. Joy (Diaz) is a high-powered commodities broker whose pasty-faced fiance has just dumped her in a humiliating way. Jack (Kutcher) is a womanizing slacker. In the film’s one example of a character’s acting sensibly, Jack’s father (Treat Williams) has just kicked the man-child out of the family business.

A hotel booking error assigns this pair of strangers to the same suite in Las Vegas, where they’ve gone to nurse their wounded egos. I will not attempt to describe the tumult of the scene in which they discover each other’s presence, except to say that in such basic matters as lighting and camera placement, it compares unfavorably with a YouTube pillow fight filmed in the dorms after Conan’s sign-off.

Feathers smoothed, Joy and Jack get very drunk, wake up married and head for divorce court, the one problem being how to split up the millions they’ve won from a slot machine. Standing between them and their money is the drearily named Judge Whopper (Dennis Miller), who nonsensically threatens to “tie the money up in litigation” forever — does he plan to sue them? — unless the couple tries to make an honest go of marriage. Under the court-ordered supervision of counselor Dr. Twitchell (Queen Latifah), the pair snipe and strategize, each hoping to end up with the whole jackpot.

This is the second writing credit for Dana Fox, the first being the forgettable “The Wedding Date” of 2005. Here Fox borrows like a magpie from a slew of earlier rom-coms, but often adds bits of meanness and infantilism all her own. The script seems especially concerned with such things as Jack’s crotch, Joy’s bra and characters with absolutely hilarious names such as Dick Banger, Joy’s hard-charging boss (Dennis Farina). For the second time this spring (the first occurs in “Baby Mama”), an inaccessible commode and a convenient sink join forces in a sinister way. At the movies, 2008 may yet go down as the year of the toilet, long foretold.

Through it all, Kutcher plays very near his sweet spot and is asked to do nothing more than work his usual transformation from randy mutt to cuddly puppy. The talented Diaz has a harder time with Joy, whose alleged drivenness and business acumen never emerge from the welter of crass gestures and hyper nonsense that the script provides as the only clues to her character.

As the film trudges past the 60-minute mark, preparations begin for the inevitable onslaught of vulgar sentiment to come. Ominous lines like this start to offend the ear: “You bet on me, and you made me want to bet on myself.” You may be forgiven if, awaking from a nap, you are confused by the sight of Joy and Jack ambling through a park, holding hands with Jack’s little niece, who appears out of nowhere to bring them together. Weren’t the grownups sworn enemies when you nodded off? Ah, but you’re forgetting the alchemy of love and the magic of the movies.

So did the people behind “What Happens in Vegas ….” (PG-13) 99 min. S