Back on the old board, I said I thought the Joker's best line ever was "Geeze, I hit Jason harder than that. His name was Jason, right?" Many disagreed with me, saying "That's not funny" from this was his best line, as well as the "a little boy in a playsuit crying for mommy and daddy" line.
I'm still going with "His name as Jason, right?" as Mr. J's best line.