That is very sad and, to be honest, morally wrong.
It's kinda like (but not quite, as you shall see..) and the young child that is playing and exclaims to their friends/family 'I'm a Spaceman!' ; you go 'Oh, ok...that's cool. You're a Spaceman..' - go along with the flow, being respectful.
Would this guy go 'No, you're just a child playing in a cardboard box. Stop being stupid' ? I'd hope not.
Identity, sexual or not, is a huge thing for everyone living and breathing. It defines who they identify with, their confidence and acceptance into this big wide world for the rest of their lives.
For someone to be so disrespectful, why it just makes my blood boil....
SJD xx