South Park - Season 15 Episode 4

Thinking the school has posted the size of all the kid's penises for the whole school to see, Cartman works all the boys up into tizzy. The principal decides it's time to address Cartman's anger issues by having him take anger management classes. Cartman uses his anger to enrage the class and hold a business hostage. Stan's dad decides to teach the students how to properly measure penis size, using complex mathematical formulas.