I just typed the whole story out but got palpitations of her printing it and hauling me into her office Monday so you'll have to make do for vagueness 
Today I followed company policy for charging somebody for something (around £20, not for ketchup or something). The man thought he should have got it for free.
He was incandescent with rage, shaking and screaming/ shouting at me. I remained polite and helpful, and gave him a free alternative that would have probably been fine. He carried on shouting, so my manager came down. She listened to his horrible words about me, apologised to him and gave him the thing for free. He gave me a lovely smirk all the way out the door.
AIBU? I'm so annoyed.