zombie84 said:It just means "the black sheep." The one who doesn't belong. Red hair is very uncommon, and being a step-child makes you a bit of an outsider, so to be a step-child with red hair would make you especially an outsider. Thats all that expression means. Its a very common expression in north america at least.
I have red hair and hate that saying.
I think seeing it about being an outsider it needs to be update to:
"I Beat you like you were a Star Wars Dork"