Dave (Jason Bateman) is a workaholic family man. Mitch (Ryan Reynolds) is a slacker man whore. Dave dreams of Mitch's commitment-free life. Mitch fantasizes about having people who actually care about him.
One drunken night, the childhood pals use an Atlanta fountain as a urinal. Their streams cross, if not their light sabers, and zap! - body-swap! Dudes and dudettes, we give you The Marriage Crashers!
Trapped in Dave's body, Mitch gets a taste of changing diapers and showing up at work. In Mitch's body, Dave gets to sleep all day and play all night.
Directed by David Dobkin (The Wedding Crashers) from a script by Jon Lucas and Scott Moore (The Hangover), The Change-Up is potty, potty-mouthed, and poopier than a nursery full of toddlers fighting toilet training.
On the plus side, Bateman, Reynolds, and Leslie Mann (as Dave's underappreciated wife) are reliably funny and Olivia Wilde (as Dave's legal intern) actually plays a human (as opposed to whatever the heck life-forms she is supposed to be in Tron: Legacy and Cowboys & Aliens).
Like the kids in detention, The Change-Up wants to offend your sensibilities. It sets new records for scatological humor and profanity. You know about the poop. Also know that the F-bomb gets fired so often you might get strafe marks. Also know that there is much stoner humor.
At the same time, the film drums the familiar beats of body-swap films such as Freaky Friday and body-switch films such as Big. These stories are about why the grass seems to be greener and how it feels to walk a mile in the other guy's shoes.
This is what Dave learns: When you have to fertilize it, the grass doesn't look greener. This is what Mitch learns: When they're a size too small, the other guy's shoes hurt your feet. The benefit of the body swap is that each fully sees himself when he's in the other's skin.
Naturally, this gives each lead the fun of playing his character and playing his character trapped in the other's. Reynolds runs the gamut from trash-talker to bashful and is as funny as he was in The Proposal. Bateman seesaws from self-effacing to scrofulous and is as out there as he is in Horrible Bosses.
Too bad the performances get flushed away in the toilet humor. The filmmakers are under the mistaken impression that in order for a gag to work, the audience should gag from the gross-out situation.