Pretend you're retarded in the elevator. Drool a little bit, cross your eyes, and make strange movements with your limbs and head periodically. Keep opening and closing your mouth as well, and stick your tongue out. That way, if anyone does try and talk to you, they won't expect much of a conversation anyways. Plus, it's fun getting good at it and fooling people. I do it on long car rides to cars that are passing us by slowly. I wave and they usually get a really sad look on their faces and wave back.