There *is* a level of not knowing "the rules" when it comes to women.
There was a day not too long ago where, in the same afternoon, I had one woman glare and turn away when I smiled and nodded at her. And then one woman who commutes on the same train I use, who'd never once looked me in the eyes in the two years I've been commuting to this job, asked me what she did that made me angry with her.
This doesn't just apply to women. People of both genders can be in a bad mood, or simply be not very nice people, or even have issues that make them unable to read social signals well. I've had both male and female people act strangely when I smile or try to exchange pleasantries (in a completely non flirting way), and I've also had men take it the wrong way and assume I want to jump their bones just because I smiled and nodded.
Or maybe some of these women have had bad experiences where they've smiled and exchanged pleasantries with a guy who took it the wrong way and started "hitting on them," or even got stalkerish. This has happened to me, and I felt all confused and guilty. What did I do to make him think I was flirting? I just smiled and said hi. Is that wrong?
If this sort of thing has happened to a woman a lot, she might be twice shy, so to speak.
Probably the best approach to dealing with women is simply to treat them as people and treat them how you'd like to be treated in their situation. You won't get a 100% approval rating, but no one does. But guys who are constantly on the prowl, who look at most encounters with women as an opportunity to "get" sex, and by any means necessary, well, that's just creepy. That attitude leads to a lot of date rape, I think.
Back when I was in college, the term date rape was only just being coined, and many guys looked at a young woman who was so drunk she couldn't maintain as an "opportunity." Absolutely despicable, and also baffling. How much fun are you going to have with someone who's on the verge of puking?
I think a lot of what these guys did was more about bragging to their friends than having fun. Guys in fraternities used to even leave their drapes open or have peepholes in their walls so their buddies could watch when they had a drunk girl in their room.
I'm married, and good GOD am I happy about it. "No means no" is easy for me to understand. That part I get. All the rest of it, sometimes it feels like a maze where I'm not even allowed to see the walls until I smack into 'em nose-first. And where the walls shift and move at random.
That's just life. People don't always get along or operate on the same wavelength, and we don't all play by the same rules. Everyone is moving the walls all the time. I remember feeling very frustrated when I was younger, because I felt like there was some rulebook everyone got a copy of that I didn't.
There is no such book. People are mostly just bumbling around in the dark (or in dim light, anyway). I think we tend to remember the misunderstandings we have with the "opposite" gender more, though, because the interactions have that extra dollop of hormones, and of course, women are a little bit (or sometimes a lot) afraid of men, since men are usually stronger physically and are perceived as being the more violent gender.
I think erring on the side of caution in romantic situations with people one doesn't know well is probably the best call. But if a random stranger on the street gets all nasty because you smiled and said hi? Shrug it off and move on.