It’s a reference to the episode "Scott Tenorman must die".
SPOILERS!!!
In the final act of this episode, Scott Tenorman and Eric Cartman are in a chili con carne competition, and to judge their dishes, each candidate must eat each other’s chili con carne. Tenorman tries to prank Cartman by putting hair in his chili, but afterwards, Cartman reveals that he pranked Tenorman in a much more gruesome way.
He indeed killed Tenorman’s parents before putting their flesh in his chili, meaning that Cartman just forced Tenorman to eat his own parents.
