If Vince Vaughn is worried about losing the world's sexiest man title to Hugh Jackman, he shows no sign of it in "Four Christmases."

Vaughn looks like he's been living on yule logs and egg nog for a while now. That doesn't make him any less funny, but if he's not careful, he's going to start getting scripts meant for Seth Rogen. It doesn't help that he's paired with teeny Reese Witherspoon, who at times looks alarmingly like an hors d'oeuvre next to Vaughn.

They play San Francisco yuppies Brad and Kate, living together and happily unmarried. They don't want any of the binding ties that have made life such a nightmare for their four estranged parents. As a rule, Brad and Kate go out of their way not to visit over the holidays, when reminders of household catastrophes they witnessed growing up are all too common.

"Four Christmases" opens with the couple on a holiday visit to Fiji that's ruined by bad weather, grounding them in the States, and forcing them to visit each of their parents in turn.

The high jinks start with Brad's father (Robert Duvall), a rural hayseed with two mixed martial artist sons (Jon Favreau, now trimmer than Vaughn, and Tim McGraw), all of whom resent Brad and his city slicker life.

The sequence is good for a few laughs, and the movie holds out the promise that successive visits to remaining parents (Mary Steenburgen, Sissy Spacek, Jon Voight) will keep upping the comedy ante.

Doesn't happen, though. "Four Christmases" generates some laughs here and there, but it's wildly uneven, and too often sets aside the generous gifts of a pretty good cast in favor of cheesy slapstick - poor Witherspoon spends 15 minutes in a moonbounce, getting body-slammed by ill-behaved children.

Probably not what she bargained for when she signed to star opposite Vaughn in a comedy that covered some of the same when-families-collide ground as "Wedding Crashers" or "Meet the Parents." This movie, by first-time director Seth Gordon, isn't made with the same skill, and doesn't start with as good a script (despite the input of four credited writers, never a good sign).

Certainly it's not the best Christmas movie featuring Peter Billingsley, who played Ralphie in "A Christmas Story" in 1983. He has a cameo here as the ticket agent who tells Brad his flight is canceled. *

Produced by Robert Birnbaum, Gary Barber, Jonathan Glickman, directed by Seth Gordon, written by Matt R. Allen, Caleb Wilson, Jon Locus, Scott Moore, distributed by Warner Bros.