Do be cautious. You can get in trouble in some places for that - I mean with the law. And whether or not the law, some employers might fire for that, wrong as that would be. Mustard is one of those that probably skirts the line of harm. It is spicy, so someone might have an adverse enough reaction.

Lemme be clear: The thief sucks and deserves that and more. I'm only worried about you.

Hopefully it all turns out alright and 'street' justice works.