yeah, it happens to me alot and i do think its because we do something to reveal nervousness....especially when i see a woman im attracted to i get nervous and any facial expression i try to communicate to her has nervousness in it as well...i feel like theres all these unwritten rules about when and where you can smile, when to make eye contact, when to make eye contact but not smile, etc etc...i probably think a bit too much about it, but it frustrates the hell outta me and i know i miss out on crazy opportunties by avoiding it...i guess the only advice out there is keep trying, because personally if i get 5 weird looks and 1 smile, its a good day for me.
Another thing is to maybe see any kind of reaction as a success, because good or bad some reaction is better than no reaction in my book