I worked for a couple of years as a psychologist in a maximum security prison, and believe me that place was hell on earth for reasons I won't go into. Imagine the worst things you think of, and then double it. Seeing just how terribly human beings can treat each other (inmates, officers, admin, every single person there) changed me forever.
But on a more light-hearted note, my best friend and I worked at the Captain's Club out at Lake Travis for its opening weekend. We started as busboys on a Friday and the owner said he couldn't pay us much money but we could eat all the food we wanted. As high school seniors that sounded good to us. Sunday it was shut down following the worst food poisoning outbreak in Texas history. Literal sewage in the water. Goodbye innards. We had a backpacking trip in Colorado a few days later, celebrating graduation, and we left every gas station bathroom between Austin and Denver a shit-covered hellscape.