Theoretically, you can pierce any part of the body you can imagine. I’ve seen photographs of piercing in shady places such as in the Achilles heal, or under the collar bone. But actually, the number of body-parts most piercers would agree to work on is pretty limited.

It’s accustomed to divide the areas of the body into two parts: natural hanging areas, and unnatural. The natural areas include every part of the body that already has a skin-fold, or a bulge; as the navel, eyebrow, nipple etc, as well as any other area where the needle can penetrate from one side into the other, without forcing the body or skin to change its natural form.
In unnatural hanging areas, we actually “create” a fold in the skin, and pierce it.
A piercing in such areas is called “surface”, since the piercing is located under the surface of the skin.
A surface will take much longer time to heal than a piercing in a regular area.
In most cases, you’ll give up after a period of time, take the piercing out – and have ugly scars. That is the reason, by the way, most piercers only perform piercing in regular areas, and avoid doing any surface piercings. The reason the surface piercing doesn’t heal as easily is simple: As flexible as your skin might be, and you can easily form folds in it – it will always try to fold back to its natural state, putting constant pressure on the piercing, that ultimately – will reject the piercing out.

Certain parts of the body (such as the clitoris, rather than its “hood”), or certain types of piercing (such as piercing the tongue from side to side), might be dangerous, and so are not recommended – even if the piercer has agreed to perform them.