The best way to do this is offline single player on Survival. Pick the map "Double Whammy" (level 6). When you spawn there will be a tank right by your spawn. Get in the tank and get as many kills as you can. The first three waves are just ants, spiders, and ticks, which will net you alot of kills. Wave 4 is the small attack spaceships and 6 wasps (a good place to boost the wasp cheeve). You should be able to kill everything in the first 4 waves with the tank. On wave 5 just let yourself be killed by the Hectors and then hit "Y" to restart and do the same thing until the achievement pops (you will restart on wave 1).