to do or say something unpleasant which makes someone who is already upset feel worse.
Having made the poor girl cry, he twisted the knife by saying she was weak and unable to cope with pressure.
turn the knife
To add to, exacerbate, or amplify a betrayal or wrong by further malicious actions. He said it was over, and then he turned the knife and said he had never loved me.
turn/twist the ˈknife (in the wound)
deliberately remind somebody of something they are already upset about, and so upset them even more: After the divorce, her friend turned the knife in the wound by saying she had always thought that the marriage wouldn’t last.All right. I know I was stupid. You don’t have to twist the knife.