Ask him questions
A few years ago, John Cleese was having a show to raise money past his divorce. Show was great, personal anecdotes, bashing the ex and marriage in general (it was fun, I'm not anti marriage, just to clear that up).
At the end of the show, he had a session where the audience would come up to a mic and ask him questions. My friends and I had gallery seats, and it took some time to gather up the courage to go down there, so I had to run. Ran trough the theater, down the stairs, and made it to the line on the mic. Most of the other guy (and gals) had some decent question, such as "My best friend just got married, got any advice?" To wich Cleece screams "PRE-NUP!!" When the guy says that's too late, Cleese just starts laughing at the guy. It was quite intimidating for a 20 year old.....
So, my turn! I had already decided on my questions, we had two questions that we used for interviews at a uni-newspaper to test creativity and general sense of humour. So I ask Cleese if I can ask him two short questions, he promptly answers that I only get one shot. So I pick the best one: "What torture instrument do you identify with the most, and why?" Cleese's face lights up, and he cracks up, letting a whole new crazy laugh out, while he stammers "C-c-orkscrew!!".
Now, I'm about to walk away, laughing myself, but then he says "Okay, fire up the second one". Now I get nervous! I just made John Cleese burst out laughing in front of a few hundred people, this is going to flop like a dead baby seal..... So, the second question: "If you were a part of an airplane, what part would you be?". Sure, not a crazy question, the first one nets better responses, but Cleese really outdid himself. He pauses a bit, builds up a grin, and says: "The JOY!--stick!". And keeps laughing while I silently move away from the microphone with a giant grin!