What are some annoying things you can do in an elevator?

When no one is in the elevator, make a tape outline of a body and splash a little ketsup in the area. Then when someone comes in, you just keep looking down at it and going "TSK, TSK, TSK".
Pretend you have a dog or child with you and keep trying to coax it in...all the while holding the doors open.
Make sound effect noises for all occasions:Ding for when the doors open, a grating buzzing noise when the numbers are pushed, say the word "scratch" when someone itches...."scratch, scratch, scratch...."