John Bender buying enough time for the club to return to the library by doing an improv basketball game.
Allison using a phony story of her being a nymphomaniac to reveal more about Claire.
Bender calling Claire out for telling Brian that on Monday, the bonds they made in detention will sever.
Claire calling him out on his utter hypocrisy and jerkish behavior right back, too. Especially given that she had mostly just been sitting there taking his abuse for most of the movie.
Brian tops them both, by noting that he and Alison, the "weirdos," can say they are better than the others by default. He says, pretty forcefully, that he would never turn on them, laughing at them behind their back. "I wouldn't, and I will not. Because I think that's pretty shitty." The thing is, Brian means it. He's already shown his character in a subtle way: he doesn't look down on Carl the janitor. If anyone is going to truly come out of this a better person, it's Brian.
"FUCK YOU!" Shouted by Bender to Vernon.
For the ones who don't like Bender, Vernon threatening him could be considered this. Especially if one felt that Bender didn't get any comeuppance for his actions.
The janitor, Carl Reed, gives an epic badass boast when Bender makes a crack at his job.
Carl: You guys think I'm just some untouchable peasant? Serf? Peon? Well, maybe so. But following a broom around after shitheads like you for the last 8 years, I've learned a couple of things. I look through your letters. I look through your lockers. I listen to your conversations, you don't know that but I do. I am the eyes and ears of this institution, my friends.
Brian's "Fuck you" to Claire. That must have taken a lot of courage, him being lower on the social ladder and all. Not to mention Anthony Michael Hall's acting. He goes from looking shocked to crying in about TWO SECONDS.