It's the one where you have to kill the enemy with your combat knife, pick up his weapon and kill him again. too hardIs that the bloodthirsty medals or killing an enemy and then killing them with their gun? I got all the combat knife challenges playing Domination.
It's quite easy. Just keep using the gun until you notice you killed the guy.
I got my 5 kills of 1 person in a row, i killed a guy camping and naturally a camping 12yo will keep coming back to there spot, so i camped there myself and sure enough he came back over and over and over.