One picture of how my costume for the volunteer haunted house turned out. For some of the time, I was standing behind a counter, with a bucket of candy just waiting to be grabbed from in front of me.

My reactions if anyone tried to take a piece:
Slow turn of head to be staring right at them.
Fast turn of head to the same effect.
Without looking, pin their hand down, bring the other up to a shush-ing gesture.

Quite effective overall, and I was listed as the creepiest guy there.