I know a Mitchell who is known as Wormz because he used to eat so much as a kid, his mother would always demand to know "MITCHELL! DO YOU HAVE WORMS?" He claims that she would give him de-worming treatments once a month because he was so skinny, but ate *everything*.
I also know a Mitchell who is known as Tan. It was a denigration - Mitchell - Hell - Satan - Tan. We were at a Catholic school so calling someone Hell or Satan was frowned upon, somewhat, so we called him Tan. It still sticks, a lot, and the fact that Mitchell is his last name, and his first name is Aaron, just makes people even more confused.