Not always true. A straight guy I work with told me he 'wasn't sure' if I was gay (i.e. he had suspected it) when most other people assume I'm straight. I had a regular customer at work ask me if there'd been any ladies in my life recently. And when I said no she said, "There's still plenty of time for that!".
Most straight women actually. Sometimes they would even ignore hints because they're scared that their bofriend or crush is gay. A lot of my female friends are still flirting with me even though I friend zone them all the time. Maybe they can sense that I'm gay but they won't care and still hope I'm bisexual.
Filipinos too. We only call a man gay if he dresses and acts like a woman. If they're straight acting and caught with another man, we simply call them bisexual. But I guess it's just ignorance.
i dont feel like it's my job to tell them. 
