Classic funny bit, from "Taxi."
Later that year came "Reverend Jim: A Space Odyssey", which introduced (Christopher) Lloyd's character, complete with a very funny scene where Jim had to take a driving test to get his cab license:
JIM (WHISPERING TO BOBBY): What does a yellow light mean?
BOBBY: Slow down.
JIM (SLOWING SPEECH) What...does...a...yellow...light...mean?
BOBBY (HISSING): Slow down!
JIM (EVEN SLOWER): Whaaaaat...dooooooes...a...yellllllllow...llllllllight...meeeeeean?
Like the Energizer Bunny finally running out of steam, they kept running the bit, with Jim getting slower and slower, and Bobby getting more and more frustrated.
Cracks me up just thinking about it!