Get as many friends into a private game of team warfare, and have them equip lancers.
Change weapon drops to custom and change every weapon to frag grenade.
Have one of your friends shoot you down while you have the grenade aiming. It does not matter where they shoot you, as the lancer weapon does not allow for 1 hit kills. When you are crawling, have all your friends group around you and press the right trigger to detonate the grenade.
Rinse and repeat until you have the achievement.