He may revel in humiliating himself on screen in over-the-top situations, but Vince Vaughn swears his best comedy is ''based in reality.'' That's why he has never done a traditional, boy-meets-girl romantic comedy. ''They always had some strange subplot,'' says the actor of the scripts he's been sent. ''I thought, 'I'd like to do one, but there's nothing out there that I'm responding to. Why not just develop something?''' And so he came up with The Break-Up, which finds the funny not in a couple's courtship but in their separation. ''The charm of the movie is it's relatable,'' says Vaughn, who also produced. ''In relationships, arguments about the garage clicker can be about so much more.''
Shot entirely in Chicago last summer, the movie stars Vaughn and Jennifer Aniston as a couple who call it quits but continue to live together in their jointly owned condo. Vaughn ''is doing what he does best,'' explains director Peyton Reed (Down With Love). ''He's playing a character who's still a boy. He's unevolved and maybe not ready for the level of relationship he's involved in.'' Aniston, meanwhile, shows off her Friends-honed comedic instincts and a whole lot more. In one scene, she struts around in the buff, desperate to make her ex jealous. Reed is coy regarding just how much bare Aniston made the cut (''You'll have to wait and see,'' he says) and is equally mum about the irony that a movie about warring former mates made lovebirds out of its stars. ''I have to plead ignorance in terms of what was going on during the [shoot],'' he says. ''All I knew was they had amazing chemistry on camera and, frankly, that was all I cared about.''