This is tough. Has to be done in co-op and Versus. The only advice I can give is stay in synch with your friends and play a lot using co-op commands that can boost it.
Set a private game in Deathmatch.
Use these settings:
Time in menu: 1 min
Round duration: 1 min
# of Rounds: 50
Map: Underground Passage B
The host will always spawn in the same location. If you have a Fight Stick, set it so that the stick is held in the upper/right direction. I placed a heavy object on the stick to wedge it into position. Then set the "A" button to autofire.
What should happen is that the host will roll to the right direction, and kill himself by falling off the map. This should end the round in about 6 seconds. In Deathmatch, you get 50 Camaraderie points per round you participate in (in a game of 2 people).
Let this sit over night and you should have the achivement by the next morning.
I've been doing this for a few days now, and I'm currently at 270,000. Going for the 1,000,000 insignia and the 5 Star Code Names.
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