I love Wikipedia definitions:
"Black sheep is an idiom used to describe an odd or disreputable member of a group, especially within a family. The term has typically been given negative implications, implying waywardness. It derived from the atypical and unwanted presence of other black individuals in flocks of white sheep."
Apparently black wool was "considered commercial undesirable because it could not be dyed." Man, that makes it sound cool to be a black sheep! As in, you can't be affected by society... you march to the beat of your own drummer.
Anyway, who was the black sheep in your family? What about your SO's family?