The Simpsons

The Simpsons is a television series which airs almost worldwide and revolves around the dysfunction titular family. It began in 1989 and is still broadcasting now. The Simpsons also exists in the South Park universe, as seen in "Simpsons Already Did It", but it would also seem at least one of the characters exist in South Park as well, as seen in "Cartoon Wars Part II". South Park has also been seen in The Simpsons.

In this Simpsons episode, "Bart of War", Bart Simpson and Milhouse van Houten are seen watching a "brand new episode of South Park". The episode features Stan, Kyle and Cartman going to a concert, and with O.J. Simpsons attacking everyone there, with Cartman having been decapitated. Marge Simpson sees the boys watching it and turns it off immediately.

Simpsons Already Did It
In the episode Simpsons Already Did It, Butters, posing as Professor Chaos, tries to get the town to 'pay' by attempting (What he thinks are) diabolical schemes such as stealing the head off a statue which results in the complete opposite of the result Butters wanted. Instead of people being terrified people think that it was done as a tribute to the Simpsons episode and many vote that it should stay like that. The idea of stealing a head off a statue originally comes from the Simpsons episode The Telltale Head.

Butters then continues to have ideas that he thinks are original but he is told by Dougie, as General Disarray, that the 'Simpsons did it' Butters then comes with a totally original idea which is to build a machine that replaces the cherry centers of chocolate covered cherries with rancid mayonnaise but then an advert for 'The Simpsons' appears on the TV with Butters' idea in the plotline. Butters then starts to see everyone and everything 'Simpsonafied,' with Herbert Garrison resembling the possibly homosexual character Mr. Smithers for example and Liane Cartman as the overweight lunchlady, Lunchlady Doris.

The other plot in this episode where Cartman, Kyle, Stan and Tweek make a civilization of Sea People mirrors the Simpsons Treehouse of Horror VII short The Genesis Tub.

At the end of the episode Chef says it doesn't matter because the Simpsons have already done everything since the show has been on for so long and has itself borrowed ideas from other shows. Butters then stops seeing the world 'Simpsonafied.'