South Park: Season 12, Episode 5

12 - 5: Eek, a Penis!

Despite receiving a sex change, the boys teacher Ms. Garrison still believes to be a man on the inside. With Garrison out searching for a way to become a man again, Cartman substitutes for the day. After the kids receive stellar test scores, Cartman is taken to an inner-city school to teach. But before he does that, he decides to change his appearance.