RHU Pet Peeve: lunch samplers.
These people go around taking food from other people's lunches and sampling them. Dude, keep your dirty ass hands out of my food! So I, and my dad, took some creative measures.
Dad once stopped a lunch thief with a nice ham, cheese, mustard, and cardboard sandwich.
I've stopped them by adding spicy peppers to my food. I have no problem eating it, but most people tend to disagree with things containing Habanero or ghost peppers.