Ruthless
(Like killers in slasher movies. They have no ruth whatsoever. Completely out of ruth. If they ever had any ruth, you'd never know it cause it's gone now. Some would say ruth-free. Slasher: now with zero ruth! Sans ruth. What I'm saying here is that any existing ruth is right out the window, or wherever it is that ruth goes when it's not around anymore. Ruthily challenged. Decidedly void of, you guessed it, ruth.)