Long plane rides are so booooooooring. Here's a traditional game that helps you pass the time. Matthew Inman of The Oatmeal gives us a primer on the rules. It's really straightforward. Now the man on the toilet must tag his playmate back.
Note that on some planes, the sign flips up rather than down.
The flight attendants usually lock the lavatories before take off and landing then unlock them once in air or at the gate. And they usually use a ball point pen to move the hidden lock/unlock mechanism.
I guess that hidden mechanism allows the crew to go in to attend to an ill passenger.