One interesting grey area I have been quite interested in when it comes to libertarianism (ahem, purely for intellectual reasons) is nudity.
I consider myself a moderate libertarian; that is to say, I do not share all the tenets of libertarianism, especially economic libertarianism, because I think it expresses significant unfounded faith in free markets.
I have preferred to err on the side of unrestricted liberty when it comes to personal, as opposed to economic, rights, because I see no problem in allowing people to exercise their personal rights, insofar as this does not infringe on the rights of others.
This philosophy has often been summed up in what is a personal favourite quote of mine — the right to swing your fist ends where my nose begins.
The interesting thing about nudity is that it is something which, at first glance, should be legally permissible. After all, who is physically or financially harmed by me stripping and walking down the street?
Yet, even in the freest of free societies, nudity is at best a limited right. You may be able to bare all on a nude beach, but probably not in a restaurant or in a government office.
Philosophically, why should this be so? Why should the right to dress as little as one likes be denied when most other rights are permittted?
Pragmatically, we can see a lot of reasons to ban nudity. For one, it would likely cause significant disorder if only a handful of people walked outside naked. (Though this of course raises the pertinent question of why these people are not charged with causing a public disorder, rather than nudity; the former, not the latter, is the offense against society, after all.)
I think, however, that the best way to philosophically explain the ban on public nudity is to classify nudity as an infringement of others' rights.
The normal reason that we allow people to swing their fists anywhere they like, provided they don't hit anyone, is that if an individual doesn't like people who swing their fists randomly, that person can just leave the vicinity.
This is not a problem for the legal system to solve, since not many people are seriously upset by fist-swinging, and not many people throw punches at nobody in particular for fun.
If, however, there were a substantial enough majority seriously upset by something in particular, and likewise a substantial minority insistent on doing that something anyway, then the legal system would have to step in.
It is all but inevitable that the legal system would side with the majority. Although this seems particularly unlibertarian when discussed in the abstract, the turmoil raised by a concrete issue like nudity would illuminate how this works.
The significant bouts of public disorder caused by nudity in itself give good cause to ban nudity; if 99% of all cases of nudity cause disorder, there's not much good reason to tolerate the other 1%.
This seems objectionable at first, but the right to be nude in public is far from essential. It can be exercised in private, on private property; there is no compelling reason, either for the survival of the individual, or of the collective, to permit people to be nude in public.
This is of course not a very satisfying answer to the libertarian. I myself do not find it completely adequate. Nevertheless, I think it may at least partially address the philosophical question of why nudity should not be a right — because it imposes significant costs on society without any significant benefit.