Well, in some societies, piercings were signs of adulthood. It can be a kind of right-of-passage thing. Some people with piercings (or tattoos) ARE masochists. Some masochists have piercings and/or tattoos. But there are also a lot of masochists with neither, and a lot of people with both who hate pain but are trying to make a "statement" of some sort. And there are some people who find piercings sexually appealing. It takes all kinds.