If you look at this stuff....go to a park or something else active
"Grunticide" - Kill 53,597 grunts total in Campaign.
82 GS.
(Grunticide and the number '53,597' are a play on the achievements in 'Left 4 Dead' and 'Prototype' (Genocide and Trail of Corpses)).
"Please Have Fun" - Kill 1,734 Marines total in Campaign.
5 GS.
(I've definitely done that one in Halo, but I think I need my number higher for Halo 2&3...)
"Da' Large Rollin' Big Shot" - Get six kills with the Shotgun within one clip.
18 GS.
[Edited on 12.24.2010 2:12 PM PST]