I believe the Warlock slap you are referring to takes a little more than one slap to the face. Same goes for the throwing knife. I personally love using throwing knives and think they are just right. Put on incendiary blade to make them burn and equip two so they become a part of your common strategy. I always look for that moment where I'm in a battle with someone, we are both damaged, I whip out a knife and finish the job. It's one of the quickest option you have when engaging a damaged player.