Had an incident last year on AA where someone boarding was giving the crew a fit because it was on a CRJ and they wanted her to check her carry on (it was large) - she was convinced that her "thousands of dollars" of makeup would melt down below. After a few of us in FC made some comments to her, I immediately went on AA.com during the flight and submitted a compliment about how professional the crew was in dealing with her insanity. She was threatening to complain, write letters, screaming, etc., and they were just as calm as could be.
I showed the FA the comment I typed up before submitting - documenting her craziness and their professionalism. He was very thankful - hopefully it helped them if she did follow through on her threats.