Oh, the Terry Gilliam animations from the TV series in general. (God, that man has a delightfully twisted mind!) If I had to choose one moment... There's a moment in the "Killer Cars" sketch where an animated siamese cat comes out and begind devouring the cityscape, as though her were Godzilla... (When I first saw that, I laughed so hard, I was doubled over from stomach cramps.)
Live action? Castle Anthrax from Holy Grail. I've watched it dozens of times, but that bit always leaves me laughing. (Carol Cleaveland never got the recognition she deserved, she was very much the forgotten Python.)
Number Two: Conform, Number Six! Conform!
Number Six: I will not be stamped, filed, indexed, briefed, debriefed, or numbered! I am a person.