You can't tell me that you haven't had a girl smile at you or something, and at least gotten all psyched.
Ah, well then, that's different. I can't tell you how many times that's happened to me. Yes, I will freely admit it. Some girl will smile at me, or something to that effect, and I'll be all "OMG". I stopped trying to talk to them after they do that, because most of the time, the response was "and what do you want?"
I've never mistaken a smile and a wave as a sexual come on. I've taken it as a hint that a girl is interested in getting to know me/talk to me, but never that they want to have sex with me or anything. That's just stupid.
I just used to randomly assume that a girl was interested in me when she smiled at me. Now, I just try my best to ignore when they do. Obviously, that's not true.