Saints Row 2

Simple solution:
Need only 2 people. The Host creates a party with Gangster Brawl selected. He then invites the 'Player' to the room and then starts the game.

Once the game starts, the Player (not the Host) quits out. The Host will get the win. No need to get any kills or let the timer run out.

After doing this 10 times, the Player becomes the Host and the Host becomes the Player.

This solution took only 6 minutes for 2 people to both get the achievement

You will need the "Corporate Warfare" DLC in order to obtain this achievement.

This achievement can be obtained in "Gangster Brawl" or "Team Gangster" brawl on either Player, Ranked, or in a Party game. Party games are much simpler when boosting for this as it does not involve matchmaking and you will only need a minimum of 2 people.

When you go to the multiplayer menu, select "Create Party" , set it to Gangster Brawl with a limit of 10 kills with the lowest time (I believe it was about 5 minutes). Invite one or more of your friends to join the party, when (s)he has connected, start the game on a map you feel comfortable with (it can be any map, personally I used "Little Shanghai and The Pyramid") , and either get one kill and wait out the timer or try to get all 10, you can modify the weapons/time/kill limit to your pleasure, as you can additionally work towards any of the non-ranked badges (http://www.xbox360achievements.org/forum/showthread.php?t=97...) while going for this achievement. Simply do this 10 times for each player and your achievement should unlock, as said by La Poison Ivy "you may in fact get it before you have won 10 matches. Do not be alarmed if you do." , having multiple people in the lobby will make each win go by faster, doing "Gangster Brawl" specifically will allow it to be a free for all, and locations of everyone will be displayed on your radar at all times.