A very early one was his appearance on the Carol Burnett show, when he starred as a strange man attempting to console Carol as a grieving widow at a funeral. After taping the sketch, Robin asked Carol if they could do it again, and the result was even funnier.
[Original line, to mourners waiting to talk to Carol] I wouldn't wait, I'm gonna be here a while.
[Ad-libbed version, same part] I wouldn't wait, I'm gonna be here a while. There's some coffee in the embalming room, but it tastes funny, be careful.
"When I became a reformed alcoholic, I realized I'm the same asshole; I just have fewer dents in my car."
His guest spot on Whose Line Is It Anyway? is widely considered one of the show's greatest episodes. Williams notably made the usually straight-faced Colin Mochrie corpse, which only one other guest star could do—Richard Simmons.
The bit about GPS devices, especially the part where Robin talks about a Scottish GPS.
I think that'd be an honest GPS. It'd go, (Scottish accent) "There's your turn! You fucking missed it, you idiot! Take one more left turn! Take another left turn! Deja fucking vu!"
His guest spot on The Graham Norton Show, where he revealed that he forgot to thank his mother in his Oscar acceptance speech, and afterwards she would try to guilt trip him about it.
Robin: (imitating his mother) So, how's the award? You came through here (gestures toward his nether regions). How's the award?
As related by Billy Crystal at the 2014 Emmy Awards, the incident when he was with Robin and Whoopi Goldberg for an event at a baseball stadium, and Robin, completely unfamiliar with the sport, became the odd one out in their conversation. Then Billy gave him the idea to make up an impression of a Russian baseball player in Soviet Russia. Now THAT he can do.