Passive-Agressive is this.
Sitting quietly watching television with your DS and DIL.
Starting to weep quietly until somebody notices.
Then, when asked if you are alright, saying "I'm fine, I'm fine, it's nothing" and refusing all offers of help, brushing off all attempts to find out what might be wrong.
Then, when they feel at a total loss to do anything to help you, you tell them about a minor non-event of a slight you feel your other DS and DIL have committed in your imagination and use it to then engineer a way to get something you want out of the DS and DIL your are currently with by making them feel guilty and sorry for you.
Or much more simply, it's saying "fine" in a way that most people, usually your DP, knows full well to mean "over my dead body and you know there will be hell to pay if you do, but I want to make my refusal look like your decision."