Crysis Warhead.
There's a tiny teeny part of a mission where you have to defend your position against waves of Alien thingys so your guy can plant C4 to blow the cave entrance in.
That's fine and all, except for the fact that the moment you try to control the turret that turns these enemies into so much mush, your ally will walk in front of the gun, or ontop of you, thereby blocking all shots towards said enemies, until they are too close and the gun then turns you and your enemy and your allies into swiss cheese. And if by some miracle your ally doesn't block your shots from the beginning, once you get to the second to last wave, they will do it, thereby stopping you from killing the monsters who are throwing big explosive balls at you.
I eventually gave up, took shelter behind the truck, and let the allies do the work until I was forced to join in. That worked fine for the most part, except for the fact that your allies will shoot the closest enemy, no matter how close, so if you're anywhere near them or the enemy, your now dead. Well done, start from the fucking beginning. I must've tried that sequence 15 times before giving up for the first night, then another 10-15 the next day.
Fucking stupidest sequence in the whole game.
The rest of it was fine though =]