What is the most inappropriate thing in The Simpsons?

The most inappropriate thing in The Simpsons is the episode "The Principal and the Pauper," in which it is revealed that Seymour Skinner is actually Armin Tamzarian, a Vietnam War deserter who stole Skinner's identity. The episode is inappropriate because it deals with serious issues such as war, desertion, and identity theft. It also portrays Armin Tamzarian as a sympathetic character, which some people may find disturbing.