I really liked the talk idiom where you first typed something rude, then slowly erased it one letter at a time, and finally typed a euphemism. Like what people use strikethrough for now, but it was funnier in talk somehow.

Only idio^H^H^H^Hnice people use talk!

Talk is great because people can complete each other's sentences and such, which is impossible with instant messaging (unless people hit send for incomplete thoughts).