There's a very thin line between pain & pleasure; clearly there are times when the line shifts. For myself there have been times when a stimulation that was previously ecstatically pleasurable, becomes painful and uncomfortable. I've heard of people who get off on body piercings, tattoos, or other bodily modifications; I doubt I would be one of them, however.

Of note, I accompanied my then lover to the piercing parlor, to have his frenum done. I was there for moral support and held his hand. The needle went through, he sprouted a powerful woody, then damn near fainted, and nearly threw up. Thank the Gods he was lying down.