For me it's Popeyes and it has nothing to do with food, just a bad experience that wasn't due to the wait staff. When I was in college, I went to Chicago for a semester and one day I decide to try Popeyes since I have never tried it before, and I do like fried chicken.
The Popeyes location I go to is downtown, and thing about downtown Chicago is there is a noticeable homeless population. Not too sound callous, but you eventually ignore the homeless asking for money when walking around. Well anyway I go to Popeyes which is in a food court like area, and I'm looking over the menu on what to get when I am approached by a homeless gentlemen.
The gentleman asked me if I could get him some chicken, and I said sure thinking I would just give him a piece off of my plate. However he wanted me to purchase him a couple of pieces of chicken which I ended up doing. So our food comes, I give him his food and he leaves. I go to sit down to start eating my food.
While I'm eating, another homeless guy comes up to me and ask he for some chicken. At that point, a police officer comes up to us and yells at the homeless guy, "I thought I told you not to come in here again." To which the officer escorts the guy out of the food court area. I ate my food quickly and got the out of there. I haven't been back to Popeyes since.