S08E19 Grade School Confidential
Martin's birthday party is predictably dull until nearly all the guests become ill with food poisoning. The only ones not to get sick are Bart (who didn't want to eat the spoiled oysters), and Principal Skinner and Mrs. Krabappel, who fall in love with each other. Bart catches his principal and teacher kissing passionately, but they immediately find out and want to swear him to secrecy. They make him his gofer, making his life miserable at school and calling him at all hours of the night (all for the reward of Milhouse inheriting Bart's poor school record). Bart eventually loses his patience and exposes the Skinner-Krabappel relationship. After rumors - most of them grossly exaggerated - begin running wild through town, Supt. Chalmers threatens to fire both Principal Skinner and Mrs. Krabappel (since the relationship is forbidden per district policy) and does when Skinner refuses to call the relationship off. Eventually, Bart convinces Skinner to stand up for himself and his new ...