I never say "That's not art," "That's not music," or "That's not literature." Those terms are too broad to ever be able to justify such a claim, and often go towards pointing out the prejudices of the person saying it rather than the subject being discussed. I prefer to critique things on more concrete terms, like "Holy mother of fuck, that looks uglier than a baboon's ass. Did you paint it with your feet? You did? Then stop it. Now." or "Your music is as banal and pre-programmed as a spreadsheet from a company that makes toilet paper." or "You write as if you were trying to fill out a Mad-Lib with a thesaurus." The creator may still be pissed, but at least we agree that it's an attempt at creativity. It's just that it sucks.