or you can call him or her "rotten apple"
But how do you say all this in Chinese?
In Chinese, the idiom that indicates the bad element in a group does not present any sheep, instead, we find a horse, but it is not black at all. Let's see it:
For those that are interested in the grammatical structure of the idiom, it is a name (horse) determined by a verb phrase. In English it would be "The horse that harms [its own] herd". In Italian it would be "Il cavallo che fa del male alla propria mandria". If you want to explain it in Chinese it is 危害马群的劣马.
See you next time, if you have any comments please feel free to write it in the comment section!