How to Obtain: Complete a Special Ops Mission Mode game with the same number of kills as your partner.
You can do this over XBL/PSN, on your own with two controllers in Splitscreen or in a Private Match with another friend. Play the first Spec Ops Mission "Stay Sharp". Once 2 people are in the game there will be a total of 34 (17 each) enemy targets to hit. Once you've sorted out your guns (pistols work best) start the course. The best tactic here is for player 1 to go through the map killing all targets that pop up until he has 17 total (number of kills are on the right side). With player 2 following behind. As soon as player 1 has 17 kills, let the 2nd player take over and kill the rest. By the end of the course and once all the targets have been shot down in the last room, both players will be on a total of 17 kills each and the achievement will unlock. Or, alternatively, go kill for kill, alternating between targets