LOS ANGELES -- If you believe the rumours, the making of Four Christmases was about as festive as turkey dinner at the Lohans.

At issue: the alleged personality clash between Reese Witherspoon (supposedly the controlling perfectionist who's never late) and Vince Vaughn (purportedly the free-style ad-libber who operates according to different time zones depending on his mood).

"I don't know where that all came from," Witherspoon says, addressing journalists at a Beverly Hills hotel. "Every co-star I work with I'm having an affair with him, about to get married, we're having a baby or we can't stand each other. You can't just get along with people and work with them. There has to be some sort of drama. We got along great."

It's a sentiment seconded by director Seth Gordon, helming his first A-list studio project after last year's critically beloved documentary The King of Kong. "There were a handful of rumours that circulated that had nothing to do with our experience on the set. My experience was that they had real electric chemistry the bulk of the time. It was really a lot of fun, actually."

How much fun it was for Vaughn remains unknown -- he skipped the media conference. But that's okay -- we'll let Witherspoon tell us how great he is.

"He's so very smart and funny, off the top of his head. He's the funniest person I've worked with my entire life," the Oscar winner says.

"We're very different. We're partners on this movie. We decided to produce it together, we rewrote it. Every day was like, 'How are we going to do this? What are we going to do now?' We had a script and worked on it very hard. We worked on it for four months before we ever went on set every day for five, six hours a day. We broke it down, threw scenes away. So by the time we were shooting, we knew what we were doing . . .

"But it's also important to create a place where that person feels free to do whatever they want to do and you can stay there with them."

In the comedy, which opens Wednesday in time for Thanksgiving in the U.S., Vaughn and Witherspoon play an unmarried upscale couple in San Francisco whose idea of Christmas is ditching their in-laws and heading to a tropical paradise.

But after being busted by unforeseen events, they're forced to visit all four groups in a single day. (Both of their parents are divorced.)

Worse, each visit exposes sore points in their seemingly idyllic relationship. Supporting players include Robert Duvall, Jon Favreau, Sissy Spacek, Jon Voight and Kristin Chenoweth.

Gordon, for one, believes plenty of moviegoers will find the situation relatable.

It certainly is for Witherspoon, who has two children with ex-husband Ryan Phillippe.

How do they approach the logistics of the season? "I think the most important thing is the children -- what do they want, what makes them feel comfortable, what makes them happy? I'm very lucky. We raise our kids to be happy and it's all about them. There's a lot of communication and being open about things. There's nothing contentious about it. It's all very go-with-the-flow."

But the film is about more than just visiting relatives at Christmas time. Over the course of the story, their characters realize they're not fully committed to each other, having never honestly addressed such issues as marriage and children.

"People grow and evolve and change," says Witherspoon, who is dating actor Jake Gyllenhaal. "It's important to stay open to whatever the relationship evolves into . . . I'm guilty of this, too; I have a certain idea of what marriage is and sometimes it doesn't work out that way.

"You have to be open to whatever comes your way in life and (know) that love takes all kinds of shapes. It's not necessarily the one you recognize."

Does that mean she doesn't plan to re-marry? "I don't know. I don't think about it much."