Yes. An unfuzzy line would imply an objective definition, and I think it's clear a such doesn't exist.

But what I meant by "explain" was more the other way around - if the intended observer can't independently identify it as art, it's not. Mostly, really, I just tend to get a little upset over the pompousness of declaring something fairly trivial you've done "art", because you can construct some platitudes about it being a commentary on some social issue.