Sherlock Holmes and Dr Watson are going camping. They pitch their tent under the stars and go to sleep. In the middle of the night Holmes wakes Watson up and says, "Watson, look up at the stars, and tell me what you deduce."
Watson replies, "I see millions of stars and even if a few of those have planets, it's quite likely there are some planets like Earth, and if there are a few planets like Earth out there, there might also be life."
And Holmes says, "Watson, you idiot, it means someone's stolen our tent."
Apparently it's the world's funniest joke. So I win.