twist the knife

Derived from the fact that the act of literally twisting a knife that is still inside someone who has just been stabbed will widen the wound and make it even more painful.

twist the knife (third-person singular simple present twists the knife, present participle twisting the knife, simple past and past participle twisted the knife)

1. (figuratively) To deliberately do or say something to worsen a difficult situation or increase a person's distress, irritation, or anger.
   • 2009, Lucy Dillon, Lost Dogs and Lonely Hearts, Berkley (2011), →ISBN, page 198:

     "And I'm not seeing anyone," she added, just to twist the knife — in whom, she wasn't sure.

• kick someone when they are down
• rub salt in the wound

• knife twister