Domino's Pizza in Boston. Here are my top 3:
This one employee would always forget to deliver orders to the right people, and they would regularly be hours late. Yet the manger believed in "second chances" (he was an ex-convict himself) so this retarded kid stayed on. Turned out he owed $40 in drug money to this local gang, and one of them came into the store and threatened to beat him up, so he took the long oven fork we had and waved it in his face. The manager broke up the fight right when he was about to throw it like a javelin. He stayed.
This drunk-as-hell lady and her drunk friends walked into the store one day demanding to order chicken wings. When I rang up the order the lady claimed she was diabetic and needed to get more chicken or her blood sugar would go down. Since my father is a severe Type-II diabetic himself, I know that chicken doesn't really affect your blood sugar, so I refused. Suddenly they all started taking pictures of me and the entire store on their cell phones, threatening to sue us if anything happened. At a loss for words, I called my manager over and told her they needed to get lost. They demanded the manager's name and as I was afraid of what would happen I gave it to them. I know. I was 21 at the time and this was my first time in such an environment. I received disciplinary action for giving out the name.
My other manager was a crazy, mentally delayed man with a sixth finger who would watch strippers in the back room on WorldStar.com while forgetting to check on said incompetent drivers, and once played Taylor Swift when I walked in because I was a skinny white kid, telling everyone that I don't want to listen to "his" music (he had it in for me from day 1). He also had gang connections in New Jersey (would always brag about the gunfights he participated in and showed off his bullet scars once), and so did his girlfriend. Said girlfriend got into a beef with one of the newer managers, and so her and her little friends started calling the store repeatedly saying they were going to jump the newer manager in the store itself. We had to call the police and shut the store down for the rest of the night while a manager from another store drove all the way over from the other side of the city to stand guard before they arrived. I quit the next day.