I saw a old guy in the post office one early morning last year who was trying to recover some mail he said he'd dropped in the box outside the night before because he'd realized that he'd put the wrong address on it.
The employee kindly told him that they weren't allowed to do that, and that in any case, that mail had been picked up overnight and was long gone to the central sorting facility downtown.
He kicked up a fuss, saying that there wasn't a pickup that early, and that she was just being lazy. She eventually told him to leave.
Five minutes later he came storming back in, now wearing a long coat, and screaming "I DEMAND THAT YOU GIVE ME MY MAIL, MY PEOPLE HAVE BEEN WATCHING THAT MAILBOX SINCE YESTERDAY AND THERE HAS BEEN NO PICKUP! GIVE ME MY MAIL!"
So he went from cantankerous old dude who wants the world run according to his convenience to crazy potentially very scary man, since he could easily have been armed, given that he went out and came back in for the express purpose of starting that confrontation.
The one postal worker very bravely stood right up to him, and the other one called the cops, and he eventually ran out of there before they arrived.