S04E16 The Courtship of Stewie's Father
When Stewie's day care instructor notes a lack of fatherly influence in his life, Lois insists that Peter take a more active role in raising his son. Not much works until Peter discovers how much Stewie enjoys it when Lois gets hurt, and soon the two are going to ever-greater lengths to torment and abuse her. Lois eventually puts her foot down, though, and Stewie feels betrayed when Peter agrees to knock it off. Can Peter ever make it up to him?