Whether a customer deserved it or not, tampering with someone's food should always be a no-no. Unfortunately that is not always the case. Occurring even in some of the classiest of places, restaurant workers share the shocking, and definitely disgusting times they've seen customer's food tampered with.
"I worked at Subway as a teenager. I had a customer who insisted on placing his order while on a cellphone. He told me he wanted a roast beef sub with 'everything.' I tried to clarify- what cheeses, what sauces, that sort of thing. He loudly said, 'I WANT EVERYTHING,' and made a snide remark into his phone about how slow you must have to be to work in fast food. So, I put everything on his sub. Literally every single thing we had behind the counter. Every kind of sauce. Every kind of cheese. Every vegetable. At the time we had a sub that came with brown gravy on it. We had another with marinara sauce. He got both, along with ranch, mayo, mustard, and, I must emphasize this point, literally every single other topping we had behind the counter. It was a huge, sloppy mess of a sub. He didn't pay much attention as I was making it, engrossed as he was in his phone call. He did later call the store, asking to speak to the manager. I answered, then set the phone down briefly and picked it up again, deepening my voice and assuring the gentleman that the employee in question had been disciplined" (Source).