A threat made by someone who has already been doing what they are treatening to do, but wants to make you think it's a new threat.
Person 1: If you don't work with me and help me out right now, I'm not going to ever help you again!
Person 2: (sarcastic voice) Woah! Is that a retroactive threat?!?! You haven't helped me out the last 6 times I've asked you. You're so lame.