I used to be in the army cadets when I was younger. One night this guy turns up, whilst we're all on a break. He knows a few of the other people there but I don't know him so I mostly ignored him. Next thing he's come up to me and my friend that I was talking to and starts asking us for cigarettes. We each tell him, in turn, that we don't have anyway. Then he asks us both again. We repeat. He still doesn't take no for an answer. By this point my friend and I are confused and somewhat concerned (he was either an idiot, drunk, or high, not sure), and it must've shown on our faces, because the next thing he asks is "are you taking the piss?"
Before either of us can answer a fist hits me in the side of the head (he'd been leaning in closer and closer the whole time, and I had already had my back to a wall before he approached, so I had no way of seeing it coming or chance to move if I had). By the time I stagger back upright I see my friend had been hit too, and the next thing one of the officers (my friends dad, incidentally) has appeared, pushed this fucking douche to the ground and is standing over him with a metal pipe ready to clobber the shit out of him.
Fortunately others restrained him before he did anything and the douche ran off, to be picked up by the police later that night. The police already knew him, he'd been in trouble plenty before.
Nowhere near as bad as some of these other stories, since there were plenty of other people there, and the douche wasn't armed, but the only time anything like that has ever happended to me, thankfully.