Most states in the US have indecent exposure laws. Some explicitly speak of breasts, others coyly cover them under "private parts".

https://www.findlaw.com/state/criminal-laws/indecent-exposur...

Yea but those laws are the manifestation of cultural mores. It used to be illegal for black people to vote so laws shouldn't be held up as universal rules of what should be right. I think the important bit is that breasts are not genitalia, and men can expose their breasts. At least for actual genitalia, no humans of any gender can legally expose them in public! That is at least fair.