When your significant other tells you you both need an exit "safe word" before you enter his dad's Christmas gathering, you know you're not in Bedford Falls. But while Vince Vaughn and Reese Witherspoon may not be "It's a Wonderful Life"'s George and Mary Bailey, "Four Christmases" is a modern holiday classic in its own right. For one thing, every family neurosis and dysfunction have taken root in the four families of Vaughn and Witherspoon's characters, Brad and Kate--and the sleek yuppie façade each has built with the other is about to come tumbling down. There are real belly laughs as the couple unexpectedly has to spend holidays with their four extended family groups. "I don't want to speak ill of your mother on Christmas," growls Howard (Robert Duvall) to son Brad, while Brad's bullnecked ultimate-fighter brothers are rassling everything in sight, "but she's nothing but a common street whore." Brad may cringe, but Kate's own family is about to mortify her in abundant ways, from her randy "Gram-Gram" and about-to-pounce cougar mom Mary Steenburgen ("I feel like a Saudi prince in here," marvels Brad as all of Kate's female relatives drape themselves over him), to the revelation to Brad that Kate used to be--how to put this--a bit on the chubby side. If the plot isn't full of surprises, the quips are nonstop and the acting believable and charming. The supporting cast also includes Sissy Spacek, Jon Voight, Jon Favreau and Dwight Yoakam in a memorable turn as the mega-church pastor Steenburgen's character is involved with. It's a comic Christmas blessing, and there'll be no need to say "mistletoe"--at least not till the viewers are home with their own families. --"A.T. Hurley"