"Four Christmases." One hapless holiday. A single humdrum movie that's more like an artificial tree than a live one oozing sap and piney perfume.

The comedy stars Vince Vaughn and Reese Witherspoon as an upscale, unmarried San Francisco couple who sneak away for vacations to exotic locales each yuletide -- Bali, Costa Rica and, this year, Fiji -- and tell their families they're doing charity work overseas.

They send expensive gifts ahead and indulge themselves with couples massages and scuba diving. As Brad (Vaughn) reminds Kate (Witherspoon), "You really can't spell families without 'lies.'"

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'Four Christmases'

2 stars = Mediocre
Ratings explained

• Starring: Reese Witherspoon, Vince Vaughn.
• Rating: PG-13 for some sexual humor and language.
• Web site: 'Four Christmases'

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But when they're caught on TV after their flight is canceled, they are forced to spend four Christmases -- both sets of parents are divorced -- with the mothers, fathers, siblings, in-laws, nieces and nephews they have avoided for years.

"Four Christmases," directed by Seth Gordon ("The King of Kong: A Fistful of Quarters"), has a few funny moments that everyone can relate to, whether it's exceeding the spending cap on gifts, letting some truths about Santa slip or being forced to relive childhood embarrassments.

But it goes downhill faster than a ski patrolman in mid-rescue and the most painful-to-watch moment comes when Brad's brothers greet him at the home of their crusty father (Robert Duvall). "Semi-professional cage fighters," they twist, punch, jump on him and use their legs like a vise to squeeze his head.

The screenplay, credited to four writers who have one theatrical release among them, also piles on jokes about Kate's girlhood weight and features characters who change long-held beliefs at breakneck speed before giving us the inevitable conclusion.

Vaughn appears to be working overtime trying to ad-lib or dress up the dialogue, while Oscar-winner Witherspoon plays it straight -- often in spiky heels that bring her a little closer to her co-star's height. Their chemistry is passable but won't set the world on fire.

In addition to Duvall, the parents are played by Mary Steenburgen, Sissy Spacek and Jon Voight, while Jon Favreau, Tim McGraw and Kristin Chenoweth pop up as siblings.

The best Christmas comedies should be like your favorite ornaments -- you can't wait to dust them off each December. "Elf" is that kind of movie. So is "National Lampoon's Christmas Vacation" and, of course, "A Christmas Story" starring Peter Billingsley, who has a cameo here as a ticket agent and is one of the movie's executive producers.

Even last year's "Fred Claus," starring Vaughn as Santa's beleaguered brother, was a funnier movie. This has been pared to 82 minutes -- the TV commercials have several lines that were cut -- but you only need to watch it once. If that.