Hit below the belt
Удар ниже пояса.
Задеть человека слишком личными вещами.
I know she really wants the promotion, but she really hit me below the belt by telling the boss about my personal problems.
I had a disagreement with a friend and he was so angry that he insulted my hair!
That was certainly a hit below the belt that I was not expecting, but he apologized after things calmed down.