It Hits the Fan
Cartman: Don't mind Kyle everyone; he's just got a little sand in his vagina.
Kyle: I do NOT have any sand in my vagina!
^ Um... that came out wrong?
Le Petit Tourette
Chris Hansen: Why don't you have a seat? (etc)
^ More from the way he repeatedly says it, not necessarily the line itself.
Professor Chaos
Narrator: Will Professor Chaos' latest plot succeed and be the final undoing of Earth? And which boy has been chosen as the replacement for Kenny? And which of these South Park residents was killed and will never be seen again? The answer will come... right now: No; Tweek; Ms. Choksondik.
^ Love how quickly they wrap it up, literally in the last few seconds.
Cartoon Wars Part II
Kyle: Do the right thing, Mr. President.
FOX President: How about I allow the episode to air but, just censor out the image of Muhammad again?
Kyle: I wish that was good enough, but if you censor out Muhammad, then soon you'll have to censor out more.
Cartman: No gay speeches, Kyle!
Kyle: If you don't show Muhammad, then you've made a distinction what is okay to poke fun at, and what isn't. Either it's all okay, or none of it is.
^ Kyle's monologue about censorship should be required viewing for anybody.
Timmy! 2000
Mr. Garrison: All right, children, today we're gonna learn about human reproduction. What do you think about that?! (class is silent) Vaginas! And penises! Butt sex! (Cartman is silent) What's the matter, Cartman? Don't you have some smartass thing to say?
Cartman: What sort of smartass thing would I say, Mr. Garrison?
^ Gotta love OOC moments.