Keyboard Assassin

(n) - An individual who furiously enters comments into a comment section for the sole purpose of proving everyone wrong, and silencing an entire thread despite neither being right or wrong, just passionate.

"Boy, that keyboard assassin sure showed me what for..."
"Reddit is fun, until a flat-earth keyboard assassin shows up..."
"4chan would be great if it weren't for all these keyboard assassins..."
"Are you a fucking keyboard assassin dude?"