In general, you should respect that someone knows their own gender and sexuality better than anyone else.
For example, if your friend came out to you as bi, it would be very rude if you replied with "well, you're actually just gay and just afraid to come out." It would be rude because it would mean that you didn't respect that your friend knows more about their sexuality than you.
You should have the same respect for anyone else. It doesn't effing matter if their identity is mogai, rare, "cringy," ace, aro, split attraction model, etc. or something you can't understand. People know more about their own sexuality and gender than you do and you should f*king respect that.
And DON'T use stupid reasoning to say that certain groups are exempt from this rule. No one's sexuality or gender is less deserving of basic respect and decency than others just for being rare.
We're people too, and we deserve respect.