Im not that into the human anatomy but wouldn't that be uncomfortable? The breasts thing.... I mean... Its DEFINITLY UNHEALTHY (Don't argue... I know ENOUGH to know that losing blood to any region of your body is unhealthy in the long run.) But does it hurt?
And why would you do it? I mean... these people are clearly just imagining the fact that its pleasurable. It can't really be pleasurable... You have certain nerves that are pleasurable... a rope around your wrists or getting smacked on the thighs isn't pleasurable. Its just that they may BELIEVE Strongly enough that it is...
Hell... I remove my own in-grown toe nail and it feels good to me to tear it out... that doesn't mean it should feel good. I just think it does.