Now that I've been following this thread for a while and I was semi-skeptical of the topic at first, I think I myself accidentally triggered a fwb's orgasm once.
It all happened one summer when we were left together after the rest of our friend group went on a long trip through Europe. We were alone, we were horny as fuck, we didn't even liked each other that much physically, but we were available and... horny as fuck, as I said.
Also this girl always talked about some ex she had a long time ago who had a true monster cock and then told "No offense yours is alright" to every boyfriend she met. That drove me nuts because I guess I was much younger and I envied that guy, and it made me want to fuck her brains out each time, as if I had to teach her a lesson or something, lol.
Anyway, so one time we were staying at some mutual friend appartement and it's pretty late. We were sharing a sofa and decided to go for a quick fuck before sleep, because that's what we were doing all the time, fucking straight out of boredom. We tried some postitions, I ate her out a bit and then I am laying on my back while she bounces on my cock. Pretty alright.
The thing is that I had just learned a technique in which I grab the base of my cock with my index and thumb, creating a cockring. You've probably seen White Pony do this in order to increase his already impressive girth. It must have taken her by surprise because we were already fucking for a short while, but that sudden increase in girth made her scream into a cushion and squirt all over me.
We fucked a ton that summer and I can't say it was good at all most of the time (horny boredom, huh) but I'm pretty sure she remembers that sudden orgasm.
) 
