he was once asked if he wrote out his material or came up with an outline before he went on stage. he said no, he just went with whatever was on his mind, sometimes even making stuff up as he went along.
one spur of the moment joke/comment i heard him make in concert was when some hot looking chick got up during his set. it was apparently cold where she was, and he said to all of us "whoa, your nipples are as hard as chinese algebra!"
a most unique skill set that could go on these crazy long rants without much preparation, and be incredibly entertaining in the process. he was like a more frenetic version of jonathan winters.