That poster is jelious of you, and something about you and your work makes him scared of you. Not that you are crazy or threatening, but you threaten to upset his apple cart.

As an artist myself, I've been invaladted perasonaly along with my work on and offline. NEVER let someones nastyness define you as an artist or as an human being! It reflects them more than you! Invaladateing one, online is common and is very cowardy.