The hardest achievement I've ever gotten? Well, actually, there is more than one. That's Just Crazy! Achievement (75 gamer-score - Gears of War 3) This, achievement, felt like forever to obtain. You need to complete Gears of War 3 on the insane difficulty setting. Now, tell me, who in the hell didn't have a problem with the last boss? Also, try getting this achievement 'solo' the whole way through. Yeah, good luck. Hardened War Hero Achievement (100 gamer-score - Call of Duty: World at War) This, achievement, almost made me go borderline retarded. You are required to complete the game on 'Veteran' difficulty. The enemies, who took grenade baseball training, threw five-million grenades a second and all of them landed perfectly near your feet. Checkpoints were a god-sent in this game. Mile High Club Achievement (20 gamer-score - Call of Duty 4: Modern Warfare) Despite unlocking this very easily now, it was almost impossible in the beginning. The last mission in Call of Duty 4: Modern Warfare almost requires one specific method to complete this monster. Advice? Use your flashbangs efficiently and effectively. This achievement almost requires perfection to unlock. Oh, and did I mention you have one-minute to do this? Good luck. That's all for now. Peace out.