The Grim Adventures of Billy and Mandy (2001)

Season 6: Episode 20

At a school fair, Grim's scythe accidentally transforms the dull Principal Goodvibes and his hippopotamus into gangster rappers, Goodvibes now calling himself Principal Goodbling. In the following, Goodbling changes the entire school to be more hip-hop-oriented, to the annoyance of Mandy. Although initially Grim likes the new style of the school principal, he later thinks Goodbling is just a poseur and goes to talk to him, but Goodbling attacks with yo-mama jokes. Irwin's grandmother, Tanya, confronts Goodbling and proves to be better than he is at yo-mama jokes that Goodbling reverts to being the boring Goodvibes.