Someone who regularly consumes mass amounts of ketamine to the point that they become permanently retarded. Ktards are known for being blissfully unaware of their surroundings and life in general. The only care about k and will stop at nothing to get their fix.
You can tell if someone is ktarded (high on k) by their blank stare, open mouth (tongue occasionally hanging out) and inability to walk, talk, move, comprehend, or do anything other than listen to drum & bass for hours straight.
Person 2: "SO definitely."
Man: "Hey Sally, suck my dick!"
Sally: "Wtf? No! I'm listening to some sick DnB, go away."
Man: "Come on Sally, I'll give you a vial"
Sally: "YES YES YES GULP"