Again, when the FA said "ok, go take an empty seat in coach - we have to leave now" there is no room for argument, whether or not you are in the right. You have to comply with a crewmember instructions or else you wind up in trouble. Such is the reality.

Well, as someone who has also suffered occasional discrimination because of my skin color/ethnic heritage (though being born/raised in LA gives me a very obvious Californian accent which usually solves the problem once I get a chance to speak) I do believe that this kind of stuff happens more often than people are willing to admit.

However, that being said, in this kind of situation I'd simply say "right, let me just write down your name for when I contact World HQ with my notice of a discrimination lawsuit."

Nothing gets people to pay attention more quickly than the fear of getting in serious trouble (i.e., JOB LOSS) for making a dumb decision that they're being called on.