Since this thread has been bumped I have a new episode to relate. Last month one of the hottest performers in my area chose me to experiment with a new toy: vibrating nipple clamps. She attached them while I was DATYing and then as she approached her orgasm she commanded that I pinch and twist her nipple HARD. I could her feel her flinching from the pain but she quickly came HARD. Afterwards she told me that it really, really hurt but the O was sooo good.
I don't know if I have a "special" relationship with her, but I am both pleased and honored that she trusted me enough for this "experiment." However, it is something that I wouldn't even think about doing without knowing absolutely that it was what she wanted.
Here's a picture of those little ole nipple clamps: