the first time I bottomed I had a sissygasm, untouched, and it was one of the best orgasms of my life. I've had a few since but it doesn't always happen, dammit.
Ive only experienced this once. Was riding this guy with a 7" thick cock and I felt i was cumming. What an orgasm, completely different feeling from j/o. Unfortunately i havent been able to duplicate it.