The millions of times in Gears of War 2 where I had to shout at the screen:
"I SHOT HIM FIRST... WITH A SHOTGUN.... HE WAS TWO INCHES AWAY FROM ME.... HOW DID THAT MISS!!!!!!!!!"
Then I watch that asshole Locust chainsaw me while I still angriliy call Bullshit.
God damn that made me angry.
Not as bad though as in Dead Space during that mission where you have to attach a beacon to an asteroid then launch it into space. I hated those gyrating machine things that flatten Isaac if he comes anywhere near them. Because they move so quick and you get delayed beyond belief when you have to stop, plant the beacon, get back up, aim then launch.... I never panick more then when I am on that bloody thing.
Of course the other moment is the on rails meteor shooting moments. You shoot one, it breaks into smaller bits so now instead of one big meteor you get many many smaller ones that do more widespread damage. Every shot just causes you more grief.