Society is kind of twisted when a guy is friendly to a girl and her first instinct is "creep". But that's how it is. Our culture has some how mutated to the point that friendly is no longer the norm, and what isn't norm is like, creepy. I'm guilty of this. I don't know how to react sometimes when a guy is friendly, whether he's physically attractive or not, friendly can just seem creepy. It's almost like the jerks seem easier to approach than someone who is super friendly. Now nice is different. For some reason nice doesn't seem creepy like friendly is. What the exact distinction between the two is... quite frankly I haven't a clue.
It is a very fine line that is nearly impossible to define. I can imagine this puts guy into some distress. If they want the attention of a girl, they don't know how to act around her. If he's a jerk, most likely she won't be interested in him. If he's friendly, he's going to creep her out and just make her run in the complete opposite direction. He can try being nice, but being nice can imply he isn't interested in her, like interested in her, and in return she will put him in the friend zone. My advice? Just quite while you're behind.

I feel bad for the fellas, I really do.

Being able to interact with the opposite sex seems like it has to be a natural ability. One either has it or they don't.