I would classify myself as a masochist, however the good and bad pain firefly mentioned is true (for me at least) not only on the level of good pain being a spanking from Master's hand and bad pain stubbing your toe on the coffee table, but also the psychological element to it. For example, i could never ever ever enjoy the pain coming from punishment. There's a psychological barrier that is telling me that i can't enjoy it because it's not being given to me for pleasure. I think that different implements work on this distinction between punishment and pleasure--for example, with Master, online, we normally use clothes pegs on my nipples during play. However the few times i had to be punished, he had me use a different kind. Now, i cannot speak for him so I don't know if he did it because the different kind produced more pain or not, but in my mind, whenever we use them instead of clothes pegs, i have now connected them with punishment.