I mean besides being sexy, whats the point of men having them?
Men and women are exactly the same in the breast area up untill puberty, if you were to give the boy estrogens, or estrogen like substances, he would then grow breasts and would end up looking exactly like a woman. This can even be done through high quantities of certain herbs. So to summerize, men have nipples, becouse they have breasts. Their breasts just don't "grow up" during puberty becouse their testosterone content is much larger then their estrogen, although over 25% of boys will notice some breast growth during puberty as their hormones fluctuate. this growth usualy receades as they get older.
I actually own a book called "Why Do Men Have Nipples?" The authors say that "During development, the [human] embryo follows a female template until about six weeks, when the male sex chromosome kicks in for a male embryo." That's when the embryo "begins to develop all of its male characteristics. Men are thus left with nipples and also with some breast tissue."
As boring as that may have sounded, it's actually a very funny book:)
How else could you pierce them?