How about instead of shutting down the people who say this with
‘You don’t just go gay’ or
‘You don’t even know who she is’,
take a second and think. Yes, there will be people who are saying it because it’s ‘cool’ now or because they feel like they need to, but I bet you anything there are people who are legitimately confused, and I can see why.
Ruby Rose is a beautiful genderfluid person, who is very attractive as a boy and a girl, neither and both. There are going to be people who feel an attraction to her who have never felt that way about a bio girl before and it’s going to confuse and scare the crap out of them.
Just, don’t generalise and make assumptions and if it seems like someone is really affected by it, talk to them