A really stupid reason.
A trading card hot pack seller on an auction website has banned me for the stupidest reason. I ordered a single hot pack from that seller a while back that arrived damaged -- because the dumbass didn't protect that pack with cardboard.
That seller was quick to issue me a refund of a little over $3, and I just learned he also banned me from bidding on his auctions because of his ignorance.
Who in their right state of mind would ban someone because they screwed up?
What's ironic is I was planning on purchasing over $600 worth of items from that seller today...