I've had several 'hands-free' orgasm/ejaculations over the years -- each time while getting fucked up my man-hungry ass by a top man who knew how to sling that dick! And I can tell you, it's very different (even more intense and lasts much longer than 'normal') ...! Wow -- I'm getting hard just remembering!!
Try Kegeling. Chicks do it to strengthen there vaginal muscles but if YOU do it long enough it will give you an intense orgasm! Trust me on this one. It's slow but very powerful!
I have never experienced on but I sounds like fun and I hope I do I will try to spend some time and see if I can make it happen.
I gave myself one some years ago by lying on my back, knees up & apart, and making the fucking motion with my hips, causing my hard cock to flop up and down, hitting my belly wth each thrust of my hips -- it took a while, and was tiring ... but it was well worth it!! That was my first -- all the others I've had have happened while getting fucked up my ass ...
