Welcomed To The Masquerade: Played with in the episode "Ass Burgers", in which a support group for Asperger's Syndrome that Stan joins turns out to be a society of cynics who think their view of the world as shit is what the world actually is, and what everyone else sees is dubbed as an "illusionary world", which is part of a plot involving aliens or whatever (they're not sure exactly what). They send Stan out on a crazy mission to liberate everyone from the so-called illusion they live in, getting him drunk in order for him to reenter the "illusion". They also claim that Asperger's doesn't exist, because why would it have a name that could easily be made fun of?
What the Hell, Hero?: In "The China Probrem", after Butters accidentally shoots a hostage in the crotch:
Cartman: Aw dude, you shot him in the dick. Butters: Huh? Cartman: That's not cool Butters. You don't shoot a guy in the dick. Butters: But I was just trying to stop him, and you said- Cartman: [faces him] It doesn't matter, Butters! You never shoot a guy in the dick. Everyone knows that! Shooting a guy in the dick?? That's just, that's just weak. I can't believe you, Butters.
Chef chews out the boys for revealing that his bride-to-be Veronica is a Succubus on the night before the wedding (which is true). It doesn't help that they were jealous of her. He forgives them after they send her back to the pits of Hell.
It's not all that rare that in as soon as season 6, Kyle and especially Stan get called out by their parents or someone else. For example, in "Fun With Veal", the adults call the boys out for "saving" the baby cows from becoming veal. You can't help but side with the kids on this, though, and this is an Author Filibuster based on one of Trey's real-life traits of not eating baby animal meat. And in "The F-Word"note the episode where the boys want to use the word "fag" to refer to a group of douchebag bikers, but get in trouble when they discover it's a homophobic slur, the school staff calls the boys out for spray-painting "FAGS GET OUT" on a wall to get the annoying Harley riders out of South Park. Mayor McDaniels does this twice, one of them during the call out.
The "All About Mormons" episode ends with the boys being called out on being mean to extremely nice people over something as petty as logical gaps in their religious teachings. Doubles as a Take That, Us.
Willing Suspension of Disbelief: Plays out the trope straight and is the main personality trait of Kyle in episode 222, a History channel Thanksgiving by subverting it; Kyle is shown to be fixated on the thought that the Pilgrims were human, thus he rants about the assumption they are aliens. As the episode progresses, everything Kyle says is a complete sarcastic succession of rants, but they turn out to be the truth; thus the episode escalates to more and more absurd heights to exhibit Kyle's inability to Suspend his Disbelief in the episode he exists in. The trope is wrapped by the end of the episode, as Kyle finally accepts the fact that the Pilgrims are indeed aliens; allowing him to live along in his universe. But is restored to his snarky self when the History Channel suggests that Ghosts might had been a part of the event as well. Because that just goes too far!
Wise Beyond Their Years: The four protagonists, despite being only 8-10 years old, are usually smarter and act more mature than most adults in the show. They usually see a problem or approaching danger first and come up with the solution for it in the end.
White Dude, Black Dude: When Cartman needs to form a band in "Christian Rock Hard", he gets Token to play bass. Because he's black. When Token protests that he doesn't own one, Cartman tells him to look in the basement. Sure enough, there's one there. When Token further protests that he's never picked up a bass in his life, Cartman tells him that he's black, he can play bass. Sure enough, he can.
Who's Laughing Now?: Played and subverted with Butters, his own attempts at revenge as Professor Chaos always fail miserably, though he manages to accompolish amazing acts of retribution for his abuse completely by accident (eg. "AWESOME-O", "The Tale Of Scrotie McBoogerballs").
Scott Tenorman pulls this on Cartman on 201 when he reveals that they both shared the same father.
Wouldn't Hurt a Child: Subverted in the case of Kenny and Butters quite often, and subverted to a lesser degree with Ike.
Wounded Gazelle Gambit: Cartman is quite fond of these as a method of manipulating his mother. He, Stan, and Kyle also pull this at least Once per Episode in Season Six, using Kenny's death to garner sympathy from their friends and family.
Writer on Board: Cartman's mom, Liane, is named after Trey Parker's ex-fiancee, who cheated on him. On the show, Liane is a promiscuous woman who has banged nearly every man in town (along with at least one woman), who is a terrible mother and a naive idiot who enables and coddles her manipulative, sociopathic son. Parker also named an unfaithful horse Liane in his first film, Cannibal! The Musical.
Xanatos Gambit: Cartman pulls one off in the season 3 episode "The Red Badge of Gayness" (The one with "S'more-flavored Schnapps") - He makes a bet with the others that he can make it so the south won the civil war, and the agreed stake in the bet is, the loser(s) have to act as the winners' slaves. When he loses the bet, he (successfully) argues that he can't be a slave because the south losing the civil war resulted in the abolition of slavery.
X Must Not Win: Kyle's feud with Cartman is usually justified given the latter's highly malicious intent. However even in petty wars, Kyle takes a sometimes disturbing extra mile to make sure Cartman's plans go up in smoke. eg. In "Douche And Turd" he and Cartman create opposing school mascots, with Kyle using increasingly manipulative methods to get people to vote against Cartman's candidate. Similarly a lot of Cartman's intentions are built around making Kyle lose.
Butters: Whoa, you sure seem with it, Eric. You must have some... ih-inspiration. Cartman: Yes, the tears of Kyle Broflovski when he loses his ten dollars to me.
To add onto the Cartman example, there are plenty of occasions Cartman comes out with amazing success and fame due to a bet with Kyle, but brushes it all off because he didn't win the bet in particular. In "Christian Rock Hard" for example, Cartman bets Kyle he can make a Platinum album before him. Cartman succeeds in making a highly successful Christian rock band, gaining enormous popularity and wealth. However once he finds out that Christian "Platinum" albums are called "Myrr" instead (thus technically losing his bet with Kyle) he flies into a rage in public, destroying the band's career.
And for more Cartman, in "Fat Butt and Pancake Head," Cartman pretends he (or his hand, at least) is Jennifer Lopez. "Ms. Lopez" creates a hit album, gets affectionate with Ben Affleck, and enjoys the wealth and fame of celebrity life via Xanatos Speed Chess. The reason is to make Kyle admit the possibility that the hand is an independent living being from Cartman and calls the whole thing off when Kyle makes even the tiniest admission. (In the episode "200," the hand is proven to be an actual separate entity.)
Xylophone Gag: Played surprisingly straight, albeit with a ukelele.
You Must Be This Tall To Ride: Cartman takes it to the extremes in "Cartmanland", forbidding anyone else from entering the park so he could enjoy the rides as often as he like, with no lines to wait in. However, his disregard for the park's other needs results in him letting in more and more people.
Tay Zonday's head explodes after the "Dramatic Chipmunk" stares him down during while waiting with other YouTube superstars in "Canada on Strike". Complete with dramatic music and everything. He manages to blow the critter's head off with his gun before he croaks.
You Say Tomato: The planetarium manager in "Roger Ebert Should Lay off the Fatty Foods" has a rare disorder that doesn't allow him to pronounce the t in "planetarium", although he seems to have no problem pronouncing it elsewhere.
When Mr. Garrison tries to scare all the "rich" people out of town in "Here Comes the Neighborhood", the "richers" scream when they see their neighbors in ghost sheets and say: "South Park is hainted!"
When Al Gore shows up looking for "ManBearPig", a Running Gag has him pronouncing "serious"/"seriously" as "serial".