The easiest and fastest way to earn this achievement is a little cheesy.
At the beginning of each game, anybody who is afk or disconnected will be kicked from the plane at the end of its path. Either get pushed out of the plane with the stragglers or mark a waypoint at that spot.
After ensuring you can find the people who aren't playing, drop near them and loot a weapon of these classes as soon as possible. Return to the people standing there doing nothing and return them to the menu screen with one or more headshots.
If you're only going for this achievement, it's time effective to quit the game and start over after you've done this.
This is also the best way to get the achievement for running people over with cars.