Existentialism and OFF (feel free to flame away)

I know there have been a few references to existentialist authors and their work, but i'm wondering has any episode of the Simpsons dealt with existentialist themes? I would imagine that Lisa centered episodes would be prime candidates for such a show.

uh, the one where homer eats the peppers is about the closest. it questions his perception of reality in that he always ASSUMED him and marge were soul mates, and he never questioned this part of his life. of course he ends up finding out he was right, the long road round.

JQM