The only really funny moments in "Couples Retreat" are bits that were clearly ad-libbed by the film's stars, Vince Vaughn and Jon Favreau.

The longtime friends and "Swingers" co-stars are credited as screenwriters, but it's more likely that their contributions to the existing screenplay and story consisted of improvisational dialogue and gags. (Dana White, who also wrote the awful "The Wedding Date" and "What Happens in Vegas" is probably the real culprit here.)

And if that's the case, they should have scrapped this script entirely and rebuilt the film from scratch. There are too many problems for them to be able to fix with their comic "riffing."

Also, while the film is rated PG-13, it's apparent that it was trimmed from an R-rated cut. They shouldn't have bothered, though. There's still enough sexual humor and other crudity to offend as it is.

"Couples Retreat" follows three married couples in various stages of dysfunction.

Dave (Vaughn) and Ronnie (Malin Akerman) have their hands full with job responsibilities and two young children. High school sweethearts Joey (Favreau) and Lucy (Kristin Davis) are only together for the sake of their teenage daughter.

Meanwhile, Jason (Jason Bateman) and Cynthia (Kristen Bell) have been unable to conceive and are now considering a divorce.

So all three couples agree to take a trip to Eden, a tropical-island resort. They're accompanied by a divorced friend, Shane (Faizon Love), who has taken his much-younger girlfriend, Trudy (Kali Hawk), along.

However, it clearly becomes apparent that the resort's staff — including the tyrannical Marcel (Jean Reno) — intend for this to be therapeutic. This vacation is not going to be as fun-and-games filled as the couples originally believed.

On the plus side, the film appears to argue in favor of faithful, committed marital relationships and constant communication.

But too much of the scripted humor is shrill and vulgar.

Also, it may be hard to believe, but this material makes us despise the usually likable Bateman.

"Couples Retreat" is rated PG-13 and features crude sexual and scatological humor (references and sight gags), occasional strong profanity, simulated sex and other sexual contact, brief violent content (fisticuffs, as well as animal violence), brief partial male nudity and revealing swimsuits, brief drug references (to the so-called "date-rape" drug), brief animal gore, and derogatory language and slurs. Running time: minutes.

e-mail: jeff@desnews.com