I flip out sometimes playing TF2 as a spy, I have no problem messing up and getting caught cloaked by someone skilled, but I rage to the high heavens if it's just some amateur pyro who holds down the left mouse button until he hits me.
CoD:WaW and the constant, every two seconds, five grenades, grenade-spamming enemy soldiers that could throw so perfectly they cut off all escape routes.
Civilization Revolution and some of the utter bullshit that the AI pulls, I have you down to one city, so you aren't getting reinforcements from another city without my seeing, but still you continue to spam riflemen units just powerful enough not to be overrun despite being totally blockaded. Oh, and knights vs. fighter planes should be an auto-win for the planes, I shit you not, I have had Zero fighters beaten by the knights of a less-advanced nation than me when I was playing as Japan.
I rage at some of the stupider, more pointless physics puzzles in Half-Life 2, why can I not just go shoot some headcrab zombie things, I don't want to stack boxes. I have nothing wrong with puzzles, I just hate dumb ones like some of HL2's.
People on L4D make me rage, it's that specific game too, it really annoys me how everyone takes it really seriously and can't laugh at something funny that happens.