"Derp" or "herp derp"; originally used by Trey Parker and Matt Stone to describe lame, lowbrow comedy (as in the Rob Schneider example), but has evolved on the Internet into a more general response to anything extraordinarily stupid or to statements of the obvious.
BEEFCAKE!Explanation Episode 102 "Weight Gain 4000"
"Respect mah authori-tah"Explanation Episode 203: "Chickenlover". Cartman becomes a cop to fill in for Officer Barbrady. The quote has been used a few more times in the show's run
I need about tree-fiddy.Explanation Episode 303: The Succubus, where the boys tried to warn chef, but instead met his parents who keep telling about the times they met the Loch Ness Monster who kept on asking for "tree-fiddy" ($3.50).
...and that (sexual harassment) makes me a sad panda. :(Explanation Episode 306, "Sexual Harassment Panda".
Hey! Meme! We don't take kindly to your type in here!
N-now, Skeeter, they ain't a-hurtin' nobody.
And if you think any of these aren't funny, then you need to get the sand out of your vagina.Explanation Episode 502, "It Hits the Fan". Cartman thinks Kyle's being too uptight about people saying the word "shit" after hearing it on the TV show "Cop Drama".
Whatever! Whatever! I do what I want!Explanation Episode 603: "Freak Strike"
If you think the ski instructor isn't becoming a meme...you're gonna have a bad time.Explanation Episode 602, "Asspen"
Simpsons did it!Explanation Episode 607, "Simpsons Already Did It", when Butters-as-Professor-Chaos is constantly reminded that his schemes to rain misery upon the people of South Park sound very similar to old episodes of The Simpsons.
RABBLE RABBLE RABBLE!!Explanation Episode 611: "Child Abduction is Not Funny"
Derp de derp (de teetily tum)!Explanation Episode 615: "The Biggest Douche in the Universe", from a parody trailer of a Rob Schneider film, which consists of almost nothing but variations of the word "derp".
Craaaaaaaaaaab people, craaaaaaaaaaab people, taste like crab, talk like people...Explanation Episode 708, "South Park is Gay". The marching chant of the Crab People, who disguised themselves as the cast of Queer Eye For The Straight Guy in order to make all of the males in South Park "metrosexual".
"DEY TURK ER JERRRRRBS!" Explanation Episode 807: "Goobacks". The people of South Park are angry that the immigrants from the future are willing to work for next to nothing, causing the more conservative townies to publicly voice their displeasure. An in-universe case, as well, as the phrase starts out as "They're taking our jobs", but through repeated use, degenerates into this. The episode "W.T.F." takes this even further.
This is what (X) actually believe.Explanation Episode 912, "Trapped in the Closet". Used as part of a Take That when explaining the tenets of the Church, most of which are indeed accurate. Later reused in Episode 1001: "The Return of Chef", replacing the Church with the more lawyer-friendly "Super Adventure Club".
ManBearPig is very real and he most certainly exists....I'm sereal, you guys! I'm super sereal!Explanation Episode 1006, "ManBearPig". Al Gore is dead serious about the existence of Manbearpig, an analog for global warming.
Captain HindsightExplanation Episode 1411: "Coon 2: Hindight". A superhero who comes to a scene of a catastrophe and only says what would have been done to avert it. It eventually caught on, with an imageboard meme inspired by it much like the ski instructor above.
Fuckin' Mint-Berry Fuckin' Crunch
"Oooh, long Johnson! Oooooh, looong John—*get hit by train*Explanation Episode 1603, "Faith Hilling"