Basically, I had a basketball coach starting in about the 6th grade who was an assistant through HS that called everybody by their last names. This caused confusion in practice when my brother started playing for the same team. So the coach took to referring to me by a nickname taken from a famous Kentucky player who was about my size, about my complexion, sported a similar haircut (at the time,) and had a similar style of play. It stuck, and I've been called "Cotton" by various people since middle school.