How do I tell my friend to stop disrespecting trans people?

@RUMBUM Some people see things in rather rigid terms. You aren’t going to change this person’s mind with logic or argument. You can maybe tell them that you understand why they might see it that way and maybe explain how it makes you feel when they say that. Or maybe in time they will expand their views and become less rigid. Try at least within yourself to feel compassion for their rigidity to the same degree you might want them to accept you for who you are.