For those that don’t fly much, you have to list your true biological gender to get through the TSA security so that is what the flight crews are legally required to call you - or they can’t let you on the plane for security reasons.
FWIW, I’m getting a distinctly Muslim vibe from Tristan
I didn’t know that, but I rairly fly on commercial planes since I have my own plane. It sounds like, from you said, the Delta Employee should have had him removed and Arrested for pretending to be somebody he isn’t.