I regularly make sandwiches with this mustard on them:

In small amounts, it gives you a runny nose. In medium amounts it makes you cry. It comes in a small tube rather than a big jar for a reason, you literally couldn't eat it if you smeared a ton of it on any food. I absolutely would use copious amounts of it if I had a food thief problem, and I don't think I'd ever have a food thief problem again.