I have two that are used all the time and several others that are used within a certain group, it's confusing.
One is Twin, and the other person with that nickname has a last name that is close to mine and every time we have our names written down somewhere, one of our last name's is dropped and we become sisters. So it became an inside joke and somehow we ended up being "twins" even though we don't look alike.
The other one is Fiz, I answer to that one all the time. I don't remember exactly how I got it, but every time I go to this local bar/restaurant, where I got it from, that's what I'm introduced as. I'm not quite sure they even remember what my real name is to be honest.