Figured I would start a thread bout this. I know I had a hell of a time getting some of them.
The one I had biggest problem with was getting a 2 kill streak while in the air. I finally got it. But I cheated to get it.

Went into a cage match with my buddy. We got it on Countdown. If you go into the one hanger that has target A in S&D and climb the boxes on the left side of the big door way if your facing it. Climb the boxes and get inbetween them if you do it right you should be "in the air" then just get your 2 kill streak and BAM you got it.