black sheep

The least reputable member of a group; a disgrace. For example, Uncle Fritz was the black sheep of the family; we always thought he emigrated to Argentina to avoid jail . This metaphor is based on the idea that black sheep were less valuable than white ones because it was more difficult to dye their wool different colors. Also, in the 16th century, their color was considered the devil's mark. By the 18th century the term was widely used as it is today, for the odd member of a group.

A disreputable or unloved family member. Since the majority of domestic sheep have white fleece, a black one would be different from the rest of the flock. And because the word “black” has a historically strong negative connotation, one of that color would be unwanted (in real life, sheep farmers don't like them because black fleece, which can't be dyed, is less commercially valuable). In the age of politically correct speech, the phrase is now infrequently used, and that's not because family members now get along in greater harmony than they once did.