At the 2012 White House Correspondents’ Dinner.
About 50-50, I’d say.
Update: OK, Jimmy Kimmel was funnier. But he’s, like, a professional comedian.
In the comments, gray calls attention to this line from Kimmel: “The difference between Rush Limbaugh and Bill Maher is that Maher knows he’s an asshole.”
Further update: I’m informed by AB in the comments that I got Kimmel’s line wrong. He said: “The difference between Rush Limbaugh and Bill Maher is that Maher’s audience knows he’s an asshole.”
Works either way.