Twist The Knife Meaning

(idiomatic) To deliberately do or say something to worsen a difficult situation or increase a person's distress, irritation, or anger.

Example: 2009, Lucy Dillon, Lost Dogs and Lonely Hearts, Berkley (2011), ISBN 9781101478752, page 198:
  "And I'm not seeing anyone," she added, just to twist the knife — in whom, she wasn't sure.