The Contradiction sketch
From "Monty Python's Previous Record"
Host (John Cleese): With me now is Norman St. John Polevaulter, who for the last few
years has been contradicting people. St. John Polevaulter, why do you contradict people?
Polevaulter (Graham Chapman): I don't!
Host: But you... you told me that you did.
Polevaulter: I most certainly did not!
Host: Oh. I see. I'll start again.
Polevaulter: No you won't!
Host: Ssh! I understand you don't contradict people.
Polevaulter: Yes I do!
Host: And when didn't you start contradicting them?
Polevaulter: I did! In 1952!
Host: 23 years ago.