One time when I worked at a grocery store, this big fat black chick got pissed at me because we were out of the discounted frozen shrimp she wanted. So she called headquarters right in front of me and reported me to whomever for being a horrible employee. A few months later I saw her working at a local Starbucks. She remembered my name and our encounter, which freaked me out, and she seemed somewhat apologetic. I made my order (I don't remember what it was), I left, and didn't think anything of it until I was in the car sipping on my drink which tasted like crap. I dumped it out and saw this thick lumpy green stuff at the bottom of the cup. To this day I have no clue what it was or what she did; for all I know she shit in my cup and filled it up.
You could of easily gotten her fired for that, I don't know why you didn't do anything about it.