Spit in your food. You think it just happens to the really bad customers. Well, I have a few stories for you. I'll post more if these do good.
1. When I worked at my old job (I'll call it the O and no, it's not Olive Garden, I swear), I worked as a to-go/food runner. I would take to-go orders, run hot food sitting in the window, deal with servers' money, get change for them, etc. It was a very tiring job but I have to say, it got me good at carrying large trays. I can hold a large tray full of food and plates in the other hand. I hated this job so much. Imagine a job where you had to carrying large boxes to and from other parts of a large building all night. That was what it felt like. I was exhausted from just 5 hours; I had lower back pain and my feet were so pained that I had to buy one of those foot massaging kits.
Anyway, there's a little background about how pissed I was every day when I got there. Normally, people were good. They were polite. Well, I had this one customer come in, acting like an asshole, smirking a stupid ass grin, telling me I got the whole order wrong (which I didn't) and he just goes on and on. At the O, we have a bread warmer. We put the trays of bread inside the bread warmer to keep them...warm. Anyhow, no one ever cleans it and butter can drip down inside and it was just gross. When this asshole came in, I knew I was going to do something but I didn't know what. I've never spit in someone's food and I don't plan on it. Then, just as I was getting bread, I knew what I was going to do. I rubbed his bread all over the inside of the bread warmer, picking up all the dried, old butter mess and the black, charred...stuff...on top. I've never felt bad for this.
2. A friend of mine, who I worked with at the O, had a table with spiteful old ladies. He told me that he stepped behind the dishwasher and licked the butter off every single piece of bread! He said that they ate every single one.
3. This is my favorite one. Two jobs ago, when I worked at a restaurant which was more like a fast food joint, a very good friend of mine has a horrible table. She said when she walked up, they just screamed at her. I saw her sucking on a tomato and when she and I made eye contact, she smiled. I saw her spit out the tomato onto his salad with the other tomato and take it out to him. A couple minutes later, she returned with a completely clean salad plate. I still can't believe that the man ate it. So from then on, all of our really obnoxious customers would get "tomatoed".
As a side note, before everyone gets in a pissy mood, I want to say that this only happened to the really mean customers and if you were a server, trust me, you probably would have felt the same. Moral of the story: Never mess with people who handle your food.