I see Carth and Kaidan have already been mentioned multiple times, so here's a new one:
Sgt. Reznov of CoD: WaW.
Now, let me just say this: I liked him at first. The starting mission with him was fairly tolerable and he at least didn't get in the way of me shooting Nazis. Then everything starts to go downhill with the subsequent missions, starting with "Their Land, Their Blood." That's when I learned of his Panzerschreck fetish, seeing as how he wouldn't stop yelling at me to use it when I got my hands on it.
The deal-breaker came in the vehicle mission, "Blood and Iron." It's bad enough that I'm in a tank and I can't see shit when I take a tank shell and smoke and debris gets everywhere on top of the red damage indicator, but Reznov takes it across the line by yelling blatantly *wrong* directions about where the enemy is attacking from.
Here's the gist of what happened during the mission:
Me: "Oh, joy. Another tank shooting me from nowhere. Now I can't see anything."
Reznov: "TANK!! RIGHT SIDE!!!"
Me: "...That tank is in front of me, Reznov."
Reznov: "TANK!! RIGHT SIDE!!!"
Me: "Dammit, Reznov, shut up! There's only one tank on the entire map, and it's staring right at me! RIGHT IN FRONT OF ME!"
Reznov: "USE THE PANZERSCHRECK!"
Me: "...Reznov, if you don't shut up, I'm going to kick you out of the tank, light you on fire, run you over, and BLOW YOU UP JUST TO MAKE SURE IT TOOK. Now, for the last fucking time, SHUT UP AND LET ME DRIVE!!"
...yeah.