You wouldn't refer to someone with mental health issues as mental. You don't refer to someone with a learning difficulty as retarded. We move on. We live and learn. Do I understand gender fluidity? Absolutely not. But then why would I? I've never experienced anything like that. If that's how someone feels and they'd prefer to be addressed as such, I have no problem with it.

I know a bloke that used to be called Bobby and then transitioned to female. More of a friend of a friend. We have to refer to her as Jennifer now. It's weird, and I slip up sometimes but I try to go along with it.