July 28, 1987 -- Crispin Glover's infamous "meltdown" on Letterman. It was largely considered a meltdown, but Glover maintains, loosely, that he was playing the role of a character named Rubin from a movie that would eventually see the darkness of theaters in 1991. No one bothered to let anyone — including Letterman — know in advance.
More here: http://en.wikipedia.org/wiki/Crispin_Glover#Late_Night_appearance
