I just read on screenit.com that in Disaster Movie, an underwear model runs, farts, and then says that she shit her pants. I don't think any of us want to pay to see this dumb movie for one scene, so if anybody could find it online, that would be awesome.
Also, in the movie, College, a kid asks a college girl if she would fart in a can for $5. It doesn't say if she does it or not though, I doubt it.