Courtesy of the Fabulous Flight Deck #2

Passenger in his middle 20´s boards the airplane, cockpit door is as usual during boarding open.

Passenger starts a little chat with the pilots, asking the most poxy question ever heard in the deck:
- "Do you know what all this buttons and knobs are for?"
- "yeap, we do" - answers a slighty nerved captain.
- "So what happens if I turn this one on?"
- "you get a broken nose"

The queen [captain] is not amused  :)