My friend says she knows when someone is gay. There's this guy that she says she knows is gay, but I don't see any "gay" in him.
1) Stereotypes may be funny, but they're rarely helpful or right. 2) People who are gay, and people from NYC, have gaydar. The intuitive, unquestioned, inexplicable, not-always-right sense sense that someone isn't straight. Does he know you're gay? Because, people are rarely hesitant to 'come out' to a gay person. If he does know, you bring the topic up with him and say, "One of my friends had a hunch...are you gay?" Anyways, hope that helped. Regards.
I would say in most cases, you don't know until you hear them say it. Gaydar is fantastic, but once again, it is speculation. If he is gay and hasn't come out to you yet, I would just suspect that he is still struggling with it, and if he's straight, well then that answers that question right there doesn't it?