black sheep of the family
Fig. A worthless or disreputable family member.
The “black sheep” is a member of a social group or family who is regarded as a disgrace and an embarrassment to the rest of the group. The phrase became popular during the 18th century and is associated with the proverb, “There’s a black sheep in every flock.”
It is believed that the phrase derived from the fact that the fleeces of black sheep were not as valuable as those of the white sheep. While the wool of a white sheep could be dyed many different colors, the black fleece was a lot more limited and, for this reason, people preferred to have only white sheep in their flocks.