Talking about the external stimulus thing, if it hadn't been mentioned I would have totally disagreed with the idea of women being able to rape men but something similar has happened to me.
I certainly never classed it as rape and still don't but I really didn't want to fuck this women at all, she was quite a few years older than me and I didn't think she was attractive in any way, however she and her hubby certainly set out to seduce me and my wife. We were young and pretty naive and they were neighbors who had come round for drinks.
Well, they had brought round some porn films as well and they were into the swinging scene, so after a while of watching and a few drinks she came on to me, rubbing me and eventually sucking me, right in front of her hubby who was pretending disgust but took my wife upstairs while she got naked and climbed on me to fuck. I can really say I didn't want to but even so I had a hard on and went through the motions, eventually pretending I had cum and managed to stop. It wasn't rape but I didn't want to do it.
The story I got from my wife was they never had penetrative sex.
Needless to say life on the estate was a bit awkward for us until the neighbors moved and we got divorced some years later.