I don't know if this counts as an "Art World Sin" but...
THE MOTHER FUCKING "TUMBLR NOSE" MAN. Holy shit. Red fucking noses EVERYWHERE. It's like every fucking, mother cock-sucking, colored drawing of every character in existence nowadays has to look like they have a damn cold like it's "rudolph the mother-fucking rednose reindeer flu season".
But hey, it's tumblr. Where everybody's a mother fucking snowflake and every made up gender with a name that sounds like something a snart blender upchucked is illegal to disprove/call out or they'll "like totally report you for gender discrimination" and call all their tumblr friends for back-up so they can help nuke your blog with no warning whatsoever.
Oh and the ones where they keep trying to draw any canonically skinny/slender/slim/sexy character fat/obese, because "that's not real beauty" or something...
That shit's horrible to art too.