How would a guy who has a crush on you act if he is jealous when you talk to other guys?

He could glare at you and look disgusted. He could give the guy you are with a dirty look or even provoke an argument or a fight. He may even just turn around and walk out on you and he may never look your way again. If you are trying to make him jealous by flirting with other guys 9 chances out of 10 you're going to be the loser. If you are serious over the guy you are trying to make jealous act like a woman and simply ASK HIM OUT! Some guys are just shy and more men out there (although some would make you believe that they are the greatest lovers God even created on earth) know diddly and are often too shy and inexperienced to know how to handle certain situations. Giving much more reason for young women to cut some guys slack and help them through the transition of their shyness to asking you out or you asking them out.

Note:

While the above answer lists some possibilities, there's a good chance there will be no obvious difference in how they talk to you. Trust me, as a guy who has had confidence troubles with girls, if you are friends he will continue to be your friend and not treat you differently. He'll probably be a lot quieter or shy if he thinks you're flirting with another guy though and will feel jealous. That would only serve to make him hide his feelings more. If it's a friend who likes you he's probably just not sure you return the feelings and things could get weird if you reject him