For one thing, most straight guys don't have any clue or understanding of gay guys, they don't get the attraction at all, don't know what criteria they are using for selecting you, if they have any at all, it's just wierd, uncomfortable, awkward, and they wonder if they should feel insulted. If there is any fear, it's fear of being put in awkward situations like that, having to deal with extra bullshit in addition to everyday bullshit, lol. Flattered wouldn't come into it unless you knew what the frig the guy was complimenting you on.. lol If a guy likes to frig sheep and comes on to you, does that mean you look like a sheep? lol (It's just as incomprehensible is what I mean, not equating the two.)
I've been hit on by gays several times, didn't know them from adam, they don't introduce themselves or ask if you are gay, so you know they are your typical male pig, they just happen to be gay, and the freaking crudeness of it was amazing, I'll spare you the details. Lots of straight pigs out there to, don't like them either, so long as they don't get in my face, to each their own. Flattered doesn't come into it, if it were a hetero situation and I was a woman, I'd want to slap the bejesus out of the fucker, same thing. Fear doesn't come into it for me, beyond having to deal with the awkwardness, but ignorant people infuriate me in general, don't want to have anything to do with them. It's interesting to get the female perspective on being hit on by jerks, but would rather avoid it.