As far as I know I've never given a woman cause for concern for her safety; I've sure tried hard not to. I was raised to be polite and chivalrous, and though chivalry may provoke some feminism concerns it's not a source of physical threat.
When times change, it can become necessary to alter politeness and feel out a new scale for it. When people are trying to do that, they tend to try to treat other people the way they'd like to be treated, which is of course an excellent general tactic. (Luke 6:31) But if you don't apply enough reflection and empathy, you can miss nuances. Like, as PerverseCowgirl mentions here, the fact that guys are typically much stronger unbalances the scales quite a bit. Many years ago, I had an experience that if I had been weaker would have been pretty skeevy; and thinking "what would that have been like if the tables were turned" really illustrated the concept of the need for reflection for me. Even with the roles as they were, it wasn't quite right.
It was during my first divorce. (And I never wanted even one!) I was pretty good looking. It was a bit before I developed knee problems, and I was really active in martial arts and in excellent shape. I'm 6'3", broad-shouldered and deep-chested, and was about 205 pounds, and I could outlift a 250 pound amateur powerlifter.
I was taking a massage therapy course for the sake of human contact. The students were encouraged to go to each other's homes and have practice sessions. A hot 120 pound blonde invited me to her place. (This is sounding like the beginning of a Penthouse Forum story.) I had talked about how my wife had left me, that I was not yet divorced, and that I didn't want to start anything new at the time. I had explained how I was taking the massage course as a safe way to get human physical contact. I specifically mentioned nonsexual.
She was a classmate that I had often chatted with. I'd been to her place for a practice session or two before. This time she scheduled it after dinner, which she prepared. That gave me a slight date vibe, so I found a way to to bring up the whole still married thing and flashed my wedding ring around. Otherwise, we just had a pleasant conversation. I was on the table first so as usual I stripped and arranged the towel over me with her out of the room. We had all the normal components of relaxing therapeutic massage, or, admittedly, a hot shagging session: soft lights, dreamy music, scented oil. Everything was normal while she did my back, and I was zoned-out relaxed and nearly asleep, as is the goal. After I flipped over, she started out with the normal stuff done from the front (We included feet and fronts of legs, upper pecs and abdomen, face, ears, neck, and scalp). I'm not sure whether I was almost totally asleep or actually asleep, also normal during a massage session, but suddenly I started back to awareness realizing that at some point she had moved from proper pectoral massage to running her flat, oiled hands over my nipples, which is not a legitimate therapeutic massage technique, and I had an erection tenting the towel. I sat up very suddenly and made an excuse that I had to go to the bathroom, then used cold water to eventually get rid of the unwanted erection. The long disappearance into the bathroom was embarrassing, though not nearly as much as the erection which she must have seen.
I didn't come to grips at first with the idea that she was ignoring my stated boundaries and attempting to initiate sex. On coming out of the bathroom, I explained that in the future, she should stay away from the nipples, as that could be misinterpreted as sexual, etc. She thanked me for the information. She finished the massage but I didn't close my eyes again. I brought it up again before I left. After I left and had time to think it over I stopped thinking it was some kind of mistake.
Now, much as I'd prefer things to be gender-blind, this was an entirely different experience for me than it would have been for her were the roles reversed. Well I wouldn't have DONE it, but setting that aside for now. I had 85 pounds of muscle on her. I did not feel threatened at all. At no point did it enter my mind that I might have trouble stopping her if she chose to keep going. I was only the tiniest bit disturbed by her actions, but I was quite a bit flattered. Thinking about it at the time, I realized that fundamental difference. If the roles had been reversed, and I had made some kind of sexual move on her during a session, and she had asked me to stop, and I hadn't, she would have been in real trouble. It'd be a really scary thought, even if in that scenario I had stopped. After all, it occurred after I'd already made my nonconsent clear in general terms.
Since the roles were the way they were, we stayed massage buddies throughout the class. I never relaxed the same way, though.
I don't think this woman intended any disrespect to me at all; our other interactions showed that. And I don't know exactly where she was going with this. Perhaps she intended to give me a "release" and thought that didn't really count as sex. Perhaps she had picked up that I didn't want a relationship but the idea of a guy who would turn down no-strings sex was so outlandish to her that she didn't get me saying it. Besides failing to come to grips with it immediately, some of my other reactions were typical. Self-doubt; maybe I had misremembered being explicit about nonsexual massage and only talked about relationships. And guilt; I felt a bit bad that I had apparently misled and disappointed her.
I wonder if it ever occurs that guys raised with no notions of chivalry imagine how they would feel flattered in such a scenario and while legitimately trying to understand a girl's feelings commit such an offense? When I've read such accounts, and the offense is forgiven, the guy always turns out to have been a real creep using it to push her boundaries. Is that because the published accounts are warnings, or does every guy pick up enough genuine politeness to know better in that way? This is important because if every guy doesn't know better, some education efforts are misaimed; if they only talk about respecting women, and some men are trying and failing to put themselves in women's shoes and genuinely think their offense is a respectful compliment, those men are being missed.
UPDATE: What happens if the woman is a lot stronger than the man? That does happen. Presumably both of them are used to the social norms requiring men to be more careful of such an offense. Is she just as guilty as a man would be, or partially excused because she's never analysed the reasons?