I've worked in the restaurant industry for 15+ years so there's plenty to choose from but one will always stick with me.
In my early 20's I worked at a sandwich shop and was working an evening shift. A guy came in, ordered a large veggie, and left without incident. About five minutes later he came back very agitated and told me I forgot to put cheese on it. I was almost positive I had, since it the cheese melts over the veggies and without it, it's a huge pain in the ass to try and close. Regardless, I apologized and made him a new one. He eagle eyed me the entire time. I finished it up, wrapped it up, apologized again for the inconvenience, and told him to have a good night.
A few minutes later, he was back again and livid. He started yelling at me."I told you it wanted cheese on my sandwich! Why can't you get this right?" I told him that i had put it on and offered to point it out to him. He put the sandwich on the counter, unwrapped it and screamed, "Where is it? Show it it me!" I looked down and saw a mangled sandwich. It was blatantly obvious that this guy had tried his hardest to pick the melted cheese off of his sandwich because there were little globs of dried, melted cheese all over it. I politely pointed out the cheddar and mozzarella cheese globs that were amongst the veggies. The dude lost his crap. After cussing me out, he picked up his sandwich, turned around as if to head to the door, but instead quickly turned back around and threw his unwrapped sandwich at me. He rough ridin' launched his sandwich at my face, yelled one last "eff you!" and stormed out. Fortunately he wasn't accurate and he ended up barely missing me. I looked at my coworker, was all like
and got back to work.
