Several times, back when businesses could stand up for themselves to a truly unruly or belligerent customer (I've since turned down management positions, because the current “give them whatever they want” attitude is abhorrent to me, and had only made bad customers worse).

There was the man who ordered an extra side of gravy, which costs fifty cents. When he realized he had been charged for it, he came back to my counter glowering. I looked over his receipt, and everything was correct. I calmly explained that yes, extra gravy costs extra, and that he was not overcharged. He exploded, cursing and screaming, in my dining room full of families. I asked him three times to lower his voice and stop cursing so we could come to a solution. He did not. So, I asked him to leave. When he refused, I gave him a choice: leave under his own steam, or I will call the police to help him find his way out. He raged that his family was still eating, did they have to stop eating and leave too? After a glance at his table, I told him no, his family is behaving appropriately and not causing a disturbance. They are welcome to finish their meal. He, however, is not, and must exit immediately. When he asked where he was supposed to go, with his family still eating, I said, “anywhere but here”. He threatened to never come back. I told him that I insisted he didn't, and as a matter of fact, he is banned. All over fifty cents.

There was a woman who asked for a free burger for her dog. I informed her that we do not offer free food for pets. She raged, saying that we should give free food for pets because pets are expensive. I apologized and repeated the policy. She huffed, did not order a burger for the dog, and tried to hand me her money, saying, “fine then, here, you little b*tch”. I said, “Ma'am, your money is no good here”. She looked surprised, watching as I used my manager override card on the register, and asked if I was giving her the food for free. I said, “No ma'am, I'm refusing service. Your order has been cancelled, and it is time for you to leave”. She screamed at me, the only intelligible phrase being “you can't do that!!!”. I merely smiled, pointed at the sign saying we reserve the right to refuse service to anyone, and closed the drive thru window in her face. She waved her arms and banged on the window until I told her, phone in hand, that I was going to call the police if she didn't leave immediately, and that she was not longer welcome and would not be served if she came back.

Those were just a couple of bad ones, but on the restaurant business, every day is another entitled jerk who wants something for nothing!