Actually there are very very few laws regarding public nudity except in cases where it'd done to harm someone such as exposing one's self to children. In areas where there are nude beaches for example there is no exemption from the law for them, they are just places that are 'understood' to be places where those of us who do not want to experience it should not go.
We as a culture have accepted that public nudity is generally not to be practiced, and we often get up in arms when it is, however it is rarely a technically illegal practice unless a prosecutor can prove it was done, or could be construed as being done, with the lewd intent of harming someone.
