Is staring at him a turn off?

Well, do you like it when guys stare at you endlessly? Kind of creepy isn't it? Some casual stares is one thing but a constant gaze gives me the notion that she is planning her next kill. This is one of those things that works both ways. Attention is great in moderation. Over do it and the person will loose interest fast.

It depends. He might not even notice unless he likes you back, in which case he might be staring too. As long as you blink, and continue to look alive, the guy will get over it. Repeated glances, though, make a guy notice. And they're a little more flattering and less creepy, I guess.

It could contribute to increased discomfort when you finally get around to talking. Glances are one thing, but a dead stare is intimidating.

Yes, very much

Yes. Talk to him instead.

If he likes you, then he's probably happy about it. If he doesn't, he'll think you're creepy.

Depends what you mean by "Stare". Looking at him shyly, or to smile quickly is fine, that's flirtatious. Gawking at him isn't.

I couldn't help but stare at this hot guy in my philosophy class, I felt so stupid everytime he caught me, but he started talking to me because of it all. He's not the kind of guy I'd date, but we're good friends, and he's hot so who cares.
Bottom line is, he didn't think I was psyco, and it worked out fine =)
But I wouldn't just stare at a guy intentionally for him to know I'm staring... That is kinda weird.