When Eric Cartman bought the pubic hair of Scott Tenorman in 'Scott Tenorman Must Die', thinking that it was the means in which to reach maturity, he makes several fruitless attempts to get revenge on Scott. In the end, Cartman creates an elaborate scheme in which he uses Scott to convince his parents to 'save' a pony from being slaughtered at Farmer Denkins ranch, while simultaneously, Cartman told Farmer Denkins that Jack and his wife were both a pair of demented pony-killers who had to be shot-on-sight. When Scott's father Jack and his mother attempt to save the pony, they are then shot to death by Farmer Denkins. While Denkins files a report to Officer Barbrady, meanwhile, Cartman gathered their bodies and then proceeded to grind them up and and feed them to Scott as chili.
The fact that his parents were murdered and that he consequently ate them, drove Scott Tenorman completely insane. In '200' & '201' it is discovered that during his time in a mental institution, Scott began to research Eric Cartman's history in the hopes of plotting revenge against him. During his research, Scott discover that his own father, Jack Tenorman, during his younger years had played right tackle for the Denver Broncos, and during the night of the Drunken Barn Dance, proceeded to have sex with Cartman's mother Liane Cartman, resulting in her getting pregnant with Eric.
It is unknown whether or not Jack was ever aware of the pregnancy. However, Liane seemed to have informed the rest of the town. Due to the fact that the Denver Broncos had been having a really good year, they all believed that revealing that Jack Tenorman having a bastard child could distract him from the football season. As such, when Eric years later, attempted to discover the truth about his father in 'Cartman's Mom Is a Dirty Slut' & 'Cartman's Mom Is Still a Dirty Slut', the entire town covered up the truth and altered the paternity results, and told Eric that his mother was in truth his father, due to her being a hermaphrodite.
After discovering this, Scott Tenorman resurrected the Ginger Separatist Movement that Cartman once created, so as to use them in an elaborate scheme to reveal the truth to Cartman in the hopes of demoralizing him. Scott's plan worked, but not in the way he intended. Cartman was horrified by what he learned, not because he had his father killed and fed him to his half-brother, but because he was half-Ginger.