the 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.
the black sheepor
the black sheep of the family
COMMON If you describe someone as the black sheep or the black sheep of the family, you mean that the other people in their family disapprove of them and consider their behaviour to be bad. `I was always the black sheep,' he says. `Everyone else stayed in New Jersey but I was the one to go.' My uncle was the black sheep of the family and we were never encouraged to talk about him. Note: Black sheep are less valuable than white sheep since their wool cannot be dyed. In addition, people used to associate the colour black with evil.
the black sheepa person considered to have brought discredit upon a family or other group; a bad character.
a/the black ˈsheep (of the family)a person who is different from the rest of their family or another group, and who is considered bad or embarrassing: Debbie is the black sheep of the family, having left home at seventeen to live with her boyfriend.Shepherds used to dislike black sheep because their wool was not as valuable as white wool.
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.