I like to play the guessing game for humorous effect, usually with rhetorical or seemingly rhetorical questions.
"Guess who just found out priceless family heirlooms sink to the ocean floor."
"Guess how many stab wounds it takes before a person stops screaming."
"Guess how much time you just lost listening to me say this."
(and, for a few "jokes" that came to mind):
"What's small, wet, and red all over?" "A dying child soldier in Africa."
"Did you hear the one about the civil rights protected by the PATRIOT ACT?" "Me neither."
"How many cavemen does it take to screw in a lightbulb? No, I am not making some reference to a Geico commercial."
"According the the Theory of Relativity, as a mass accelerates... Meh, I'll skip to the joke. Take a walk around the block and drop a few pounds, fatty."