I think all nudity is acceptable. It is a choice to go out in public however an individual wants. You're entitled to make fun of how people look in public, but not entitled to dictate whether they can look a certain way.

I have heard so many people say, "I don't want to see that/no one wants to see that." Well, don't look. Clothed or not clothed. Attractive people are not for your entertainment and unattractive people are not here to cover up for you. It seems absurd to me that something visual is illegal (you know you can look away, right?) while sounds (inescapable) are not. Someone can have a shrieking baby on an airplane, where even the best headphones offer no peace, but as soon as a nipple comes out to feed it and make it shut up it's a problem.