if you have a blister on your hand(usually from burns) you can always just put some beurre blanc or mayo on it and pretend that it just popped. then eat it!
Hide a coffee creamer pod in the palm one hand (the little single serving cups with the peel off lids). peel back the lid so it's almost open, but still sealed. it should burst with a light squeeze.
Pretend you have a speck of something in your eye.
Grab a fork with your other hand and act like you are going to try to scrape the speck out. Cover your eye with the "creamer" hand, with the creamer concealed behind your hand, so they can't see what's actually happening to your eye. Then puncture the creamer cup with the fork and act like your eye just burst.