South Park and satirical adult animation

This week in class we watched the South Park episode "Terrance and Philip in Not Without My Anus".  While it is regarded as one of the most hated South Park episodes ever, it sparks the conversation of how much crude humor should be used in cartoons.  The main point of the episode was to prank the viewers into thinking the cliffhanger of the last season was going to be answered, but rather being delayed by the inclusion of the Terrance and Philip special.  Terrance and Philip's characters don't have much substance to them, primarily relying on fart jokes and foul language to entertain the viewers.  Creating an entire episode based around characters like this was not a smart move in my opinion.  Nevertheless, the episode's message about inappropriate humor in television is the main conflict in the South Park movie "Bigger Longer and Uncut".  What makes South Park such a special piece of animation is its ability to mock and criticize just about any religion, celebrity, business or current events, which other shows wouldn't dare explore.  South Park has had episodes openly poking fun at abortion, racism, the disabled and censorship.  Creators Matt Stone and Trey Parker were even threatened by Al Qaeda for including an uncensored depiction of the prophet Muhammad, which the two use in their favor in a later episode.  The subject matter in some episodes is truly astonishing, and it's pretty clear that this type of satire will be exclusive to animation for many years to come.  Which episode of the show do you all think pushed moral boundaries??