I remember having no problem the first time I asked a guy out. You should take this route—especially since his sexuality is up in the air.But it was a simple matter because I knew he was gay. You want to ask a guy out but you do not know if he is gay. The answer is very simple: Ask him out without asking him out. Invite him out to do buddy things—a movie; a game of pool; happy hour; a game of Wii—basically, things friends do. I'm a fan of developing relationships as friends first (eventually evolving into romantic friendships, then exclusive dating, then more, etc).
Then hit him with the invite to do friendly activities.
The idea isn't to seduce him, but to become friends, as you would with any other friend.
You'll build a mutual trust as your friendship grows.
Soon afterward you can brush the topic of sexuality. If he's gay or bi, then he'll response with a disclosure of his own - if he is ready to come out and willing to share it with you.
Keep it vague at first by just mentioning gay things, like the latest gay marriage news or gays in the military or your "gay friend" from high school. If he's not, and worth anything as a human being, he'll stick by your side and at least be your buddy.
Worst case scenario, he is not, and you're better off without him. You like him, so consciously or not, you've built a fantasy in your head about you two being together.
Sexuality, friendships and relationships are not quite that transparent.
Keep an open mind for an infinite amount of scenarios: He may be gay and not ready to come out; he may be gay and is just not into you; he may be straight and a homophobe; he may be straight and gay friendly; or he may be gay and into you.
Don't focus on your wants right now; focus on what is.
It's more difficult for us gays sometimes, because we have to assess sexuality and then spit our game to get a date.
Most of the guys use this strategy in the gay scene, also because, mostly they are looking for sex, although they don't admit it.