the correct response when someone asks you if something is art is to loudly and exasperatedly cry out "oh my god who gives a shit?". you may adapt the oh my god part as per your personal proclivities on that matter, but do emphasise the who gives a shit part

if, on reflection, you *do* give a shit, interrogate why. what property of "being art" is relevant here? if the question is "should this be in a museum?", ask yourself what goals you are trying to accomplish by putting things in museums, what other things could be there instead? if the question is "is this artistic nudity or just porn?" ask yourself what aspect of artistic nudity makes it different from porn and why the distinction matters.

but first, always, ask who gives a shit. because perhaps you don't and you can just move on.