Well, I've seen this on other forums, so why not here? The idea is simple, someone posts a riddle (I'll start), another person posts the correct answer to the riddle and finally, that person posts another riddle for us to answer.
If no one can answer the riddle, the original poster can either reveal the answer and post another riddle or give his turn to someone else.
Here's a dumb one, but I personally found the answer amusing.
Two men are in court, accused of murder. After collecting enough evidence, the judge says to one of them "Even though we're completely certain that it was indeed you, who comitted the murder, I'm afraid we have no choice but to set you free". Why did the judge say that?