Is it really that hard to write and direct a romantic comedy involving people who are free-thinking and likable? Most films in this genre are so formulaic from a plot standpoint that, really, all the filmmakers have to do is not insult the audience's intelligence while pairing together two characters who are pleasant enough to be around for a couple hours and who the viewer wants to root for. "What Happens in Vegas" gets one—and only one—part of this equation right. Director Tom Vaughan, with the handy aid of scripter Dana Fox (2005's "The Wedding Date"), have created lead protagonists so unbearably dense and irritating that, yes, you want them to get together in the end. Twats like these two deserve each other.

Just-dumped New York businesswoman Joy McNally (Cameron Diaz) and just-fired Manhattan woodworker Jack Fuller (Ashton Kutcher) grab respective best friends Tipper (Lake Bell) and Hater (Rob Corddry) and separately head to Vegas for a weekend of frivolity. Said frivolity ultimately gets out of hand when Joy and Jack meet, drink too much, and wake up the next morning betrothed. Their plan is to get it annulled, but when Jack uses Joy's quarter on a slot machine and hits the $3-million jackpot, the two end up in court fighting over the money. The stern judge (Dennis Miller) sentences them to six solid months of marriage. If they live together for that length of time, visit a marriage counselor each week and genuinely work on their relationship, Joy and Jack will get to split the winnings. So-called wedded bliss, however, is far more work than either of them bargained for.

The very premise of "What Happens in Vegas" is beyond asinine. How hard would it have been for Joy and Jack to have agreed right from the start to split the money? That is what any sensible person would do, especially since it was obvious that the cash rightfully belonged to both of them. Instead, the viewer is offered up an ingloriously strained and unfunny sitcom situation where Joy moves in with Jack (that he is jobless and still manages to live in a spacious New York apartment makes no mind) and the two of them come to blows over just about everything in their lives. Watching these insufferable jerks argue, fight and attempt to thwart each other so that they can get the whole sum of money isn't humorous, it's only miserable. Gags involving urinating in the sink, disinfecting a dirty bed, pouring popcorn on one's privates, and violently racing to reach their marriage counselor first are limp and uninspired. The film's biggest laugh (out of a total of about two funny moments) comes when Jack purposefully gets a black eye and tries to suggest to Dr. Twitchell (Queen Latifah) that he is the victim of spousal abuse.

As is typically the case in romantic comedies, even blackened ones like this, the sparring partners eventually must start to get along and like each other. This isn't to be believed here because they don't appear to have anything in common. Jack and Joy have virtually no hobbies, no interests and no discernible characteristics beyond what is learned in their introductory scenes. Chemistry between Cameron Diaz (2006's "The Holiday") and Ashton Kutcher (2006's "The Guardian") is shiver-inducing for so long that it never rebounds when they do connect on a more sympathetic level in the third act. Diaz and Kutcher are both capable of having fun onscreen and aren't afraid to look or act goofy for a laugh, but they get close to none here. The material is surely clunky and plodding, but it isn't clever, and the single five-minute interlude that does work—Jack unpredictably turns his back on a chance to out Joy's lies to the company she works for, and the two finally see each other in a brand new light—is so warm and sweet that it feels like it's from a different, better movie. Of course, the magic is ruined quickly afterward as another tedious and unnecessary conflict breaks out.

A film with the word, 'Vegas,' in the title promises to at least have some attractive on-location shooting, but "What Happens in Vegas" even botches that. The early scenes in Sin City might as well have been filmed on a backlot (and probably were), and the story otherwise takes place in New York (how original!). There are a few ideas of potential, like Joy's growing distaste for a job she realizes she doesn't like, but these aren't dealt with in a serious or particularly realistic fashion. With the game Cameron Diaz and Ashton Kutcher left to flounder in unforgiving roles, and supporting players such as Lake Bell (2008's "Over Her Dead Body") and Queen Latifah (2008's "Mad Money") asked to alternately look disapproving and bored, the movie distastefully bides its time on the way to a happy ending of sorts. Yes, it's an conclusion that would have been reached by the twenty-minute mark had the characters been written with half a brain, but never mind. "What Happens in Vegas" is so moronic it almost makes the recent mediocre "Made of Honor" seem sophisticated by comparison.