McCarthy's character Diana steals the identity of Bateman's Sandy Bigelow Patterson, and throughout the movie they brawl over his attempts to stop her - with each star throwing real punches.
She tells U.S. TV host David Letterman, ""I was like, 'Oh, we'll do stunt stuff, somebody (stunt coordinators) will coordinate this, they'll do magic.' Turns out the magic to making it really look painful is you just actually beat the bejesus out of each other. That's the big secret I learned this summer (12) - you want it to look like you really get hit and are hurt, I just have to take a pop in the face.""
As a result, they both walked away with minor injuries.
She continues, ""I may have lovingly given him two bloody noses. Don't feel bad for him! Don't feel bad for him! We did a scene where we're fighting at the car... and I wiped out so hard, I fell about five feet... (Director) Seth (Gordon) yells cut and then Jason bursts out laughing at me and goes, 'What did you slip on?' Like I'm a total jack**s. And I said, 'Why don't you go look at the tape and then maybe you can tell me what I've slipped on?'
""He goes back and I just hear him behind the monitor going, 'Oh my God, I'm sorry, I'm sorry,' and he comes running back - in the adrenaline of the fight he had just grabbed me with both fists and slammed me down to the ground.""