Orenthal James "O.J." Simpson, (nicknamed "The Juice") is a convicted felon and former actor and football player, who murdered his ex wife and friend but was found not guilty.
O.J. appeared in an episode of South Park that Bart and Milhouse watched, going on a stabbing spree where he killed Farty the Crippled Robot, Steve Guttenberg, Callista Flockhart and Eric Cartman. He then posed for the camera with Cartman's severed head impaled on his knife, declaring that he was going to look for the real killer.
Marge said that the ongoing scandal with Mayor Quimby was the most exciting one since "The Juice was on the loose". Lisa then corrected her, saying that he was still on the loose, which frightened her.