It's a really Weird Problem?

Im a 20 year old female, in college. I am a very friendly person. But I have noticed I have more guy friends than girlfriends. I don't mind that at all. I am ok with guy friends but the minute a guy friend asks me out or any guy for that matter, I start disliking them. I act very rudely towards them, I don't know why. Most of the guys that have asked me out are great guys. I dont know why I act this way any ideas?