When Justin was telling Peter what happend at his last cheerleading tryout (he had to lift that "over weight girl" in the air) she said "I'm not wearing any panties" but wnen she was running up to him her dress kinda came up and reveiled her white underwear!
This is totally untrue and she says no such thing on the Widescreen 2004 DVD release that I have. This topic was addressed by the director/writer is his hidden commentary, but never made it to the film.
from your descriptions "2004 DVD release" and "I've seen this movie 100 times" this must meen that you love it, infact, you must love it so much that you refuse to admit its mistakes. she does actually say that. When she gets ready, he puts his hands on her hips, she puts her hands on his hands, turns her head to the right and says "im not wearing any panties". so therefore, this guy is right, and it is a slip up.
In the Widescreen DVD Edition, they mentioned that when they originally made that scene they were gonna have the girl fall and have his hand get stuck up her butt and he couldn't get it out. They took it out because they said it was too much.
I just got the un-rated DVD version, and she does actually say it. I'm not sure if it's becasue it's the un-rated version or not, but it has that in there.