G-Force

You should also get the 500 kills by playing through the game. You should try knocking out the weapon specific kills while going for this to save you some time. If you don't get 500 kills by the RDV Escape level, save your game right before the level starts and complete it. Once you're done, reload your save that you made and complete the level again. You get about 50 kills each time and it is one of the quickest missions in the game.

If you kill every enemy you meet, you will get this achievement before you rescue Hurley from the Waffle Irons...

If you don't get it before then, just keep killing enemies, as it's due to pop somewhere near that point.