You can get this achievement doing a Small FFA but it is much easier doing a Large FFA. The difference between the two FFA modes is that on Small you have a 10 kill, 10 minute limit while on a Large FFA you have a 15 kill, 15 minute limit.
If you only have one other person boosting this achievement with you you will need to kill that person 9 times then commit suicide with your grenades 9 times. The trick to getting the achievement with a 10 kill limit is to kill your boosting buddy and yourself at the same time with a grenade. Line up together, toss the nade just in front of you, and both of you run on top of it. You will finish the match with 10 kills and 10 deaths and get the achievement.
Ideally this is best to be done with 3 people; however, I got this achievement with only one other person. With only two people the last grenade must be timed perfectly or only one of both will register which will net neither the 10 kills nor the 10 deaths for both players and no achievement.