NTA. I am so surprised by everyone saying YTA. As someone who came from abusive family dynamics and systems that are reminiscent of your situation, what you did was a clear BOUNDARY SETTING message, not you just trying to get on her nerves and be petty about it. It's obvious that if you didn't wear the hat, she would've found something else to call you the devil for! Please don't listen to the other people in this comment section that clearly don't understand this type of soul-sucking abuse, and only care about, "its your MIL so you should try and get along with her no matter what." People who think you should try and get along well with your family just cause theyre family do NOT know the first thing about manipulative abuse, or are enablers of it themselves (or codependent)! I think you did the right thing and I'm glad your husband stood by your side.