Yes, it is annoying. I think it’s even worse than someone pretending to be Polish or whatever because pretending to be Polish would rarely cause other people real pain. Someone who (as andygirl put it) is portraying themselves as being gay or bisexual and is motivated by something other than “love/lust/confusion/curiosity” is guilty of what I would consider one of the lowest kinds of emotional manipulation.
(I know, I just threw the Polish thing in there…)
To me, the idea of the hip, trendy bisexuality is kind of crass-not only through manipulation (and that, in my opinion, sucks), but it’s kind of making sexuality out to be something silly, or trendy. It’s culture appropriation at it’s worst, and it’s kind of demeaning as well.
It’s probably a lot like a woman or man finding out their husband/wife is gay after years of marriage. It hurts and you feel lied to. Not that that’s necessarily the same situation, but it’s the same kind of feeling-he/she used me.