So, state laws and local ordinances. Here’s where the real stuff happens, because even in states that allow bare-chestedness these are the laws ill-informed police officers are going to use to try to get you to cover your breasts. Many police know their laws and get it right. Some don’t. Be patient with them if you can. It helps me to believe they are trying to get it right.
State laws are sometimes very clearly worded (Delaware, for example, which defines indecent exposure in males as genitals and anus, and in females as genitals, anus and breasts) and sometimes very vague (Maryland simply says indecent exposure is a misdemeanor but does not define which body parts are indecent.) Know what your state laws say.
Next try to find case law in which a female has been tried for being bare-chested. These can be hard to find and seem to almost always involve some form of formal protest or demonstration. The police I have talked to (and it’s a lot) almost always say they will ask a woman to cover up before arresting her. If she refuses, they can then claim that she is failing to comply with a lawful order or committing disorderly conduct (neither of which will probably stand up in court, several police have told me, but by then the woman has been arrested and had to pay for the expense of her trial.)
Usually people charged with indecent exposure have been doing something else asinine while also being “nude” in some way (remembering our argument that female bare-chested is no more “nude” than male bare-chestedness,) usually drunkenly assaulting a police officer, urinating in public, or having sex in public. The indecent exposure charge is almost always tacked on to other charges, and often dropped before or during the trial. Case law is important because it sets precedent. So if one judge has found bare-chestedness to be indecent, the next judge will have to at least consider that when making her/his decision. Legal precedent is one factor, not the only factor, but it pays to know what the courts have done with it in the past.
Police, I have found, don’t know much about case law and often don’t know the language in their own statutes. This is understandable. They are not lawyers and laws are ever-changing. It’s a tough job and they are doing the best they can. Knowing case law, however, is a huge help to me. I email myself the cases so that when I need them, I simply pull out my phone and have the information available. It has neutralized objections on several occasions, if for no other reason the civilian or police objector realizes I am prepared and knowledgeable. My demeanor when I walk is light and carefree (because I feel that way) so when I respond to emotional protests with calm and quiet information, they usually don’t know what to say in response!