I don't really understand what you're saying to be honest? All the gay people I know define their identity by how they feel, yes.
Of the thousands of people I know (gay or straight) only one of them sees their sexuality as an identity. She's a straight woman who thinks she's gay man and makes a huge fuss about her identity.
Everyone else I know just is gay, bi or straight.
Because if so in my school they didn't need that sort of proof to bully someone - they absolutely bullied people just because they were perceived as gay, even if they weren't.
Mine too, that's my point. They were bullied because people thought they were actually gay, not because of some internal sense of identity.
School are so much better these days. I've not come across a case of homophobic bullying in years (that's not to say all bullying is gone but homophobia is much better). What I do see is kids who are desperate for attention and telling everyone about their 'identity' who get unpleasent comments in the same way that socially awkward kids got picked on when I was a child.