Please allow me to share the last time I was hit on by a woman:
I was with my sister, and we were in a Hot Topic screwing around. I decided to buy something, so I went to the counter with my item. The cashier was female.
She was all like "Oh, that's cool that you like that", and such, and we made alittle small talk. Then I paid for my item and left.
After leaving, my sister tapped me on the shoulder and said, "You do realize she was hitting on you, right?".
*cue me blinking blankly* "Really?"
So... yeah, I'm pretty dense when it comes to that sort of thing. I likely wouldn't even notice unless they were being EXTREMELY obvious about it. But, should I somehow notice, I'd probably just get really shy.
I wouldn't act like that guy did, that's for sure. Even if I didn't find the girl particularly attractive, laughing it off like that is a serious dick move.