the black sheep of the family表示家庭的害群之马，败家子的意思。

【例句】
He became the black sheep of the family after he went to prison.
自从他进监狱后，他就成了害群之马。

Don't be surprised that he doesn't want to take over father's business, he's always been the black sheep of the family.
别惊讶他不想接管父亲的生意，他一直是家里的败家子。