I think I know this guy!

When he banked with us, my boss, more even tempered than me, sat down with him and told him that he had been rude to our staff and caused a disturbance on a number of occasions. He explained that, if there were any future instances, we would ask him to close his account.
He was absolutely flabbergasted. He couldn't believe the bank would consider terminating the relationship just because he abused "the help." In any case, he behaved from that point forward.
What's enough provocation is obviously a matter of judgment, but the choice is yours.