This is driving me crazy

I'm trying to think of the name of this movie where the guy cheats on his girlfriend and then hides the girls underwear in the toilet top... and she finds it and asks him and he tells her its a present for her and he got it out of a bin. Can anyone help me???? thanks.

The movie is A Guy Thing. The guy in it hasn't cheated on his girlfriend, though; it only looks like he has. Also, this thread has been moved to the more appropriate Movie Questions forum.