probably this one:
round at my mates, playing cod4 on his ps3 (the television studio level I think?) I got down to sudden death, 240-240 at the end of the game. There was me, one other person on my team versus 6-7 people on the other side, so I did what any right-minded gamer would do. Pulled the pin out of a grenade, ran into their respawn point and KABOOOM'ed on their asses. Killed all but one who was last standed, and my teammate just fragged him round the corner.
...mind you, I've got one from splinter cell 1 that qualifies as well I suppose...
The level where you first learn to rappel and land in the kitchens (forget what it's called) you aren't allowed to kill anyone. I snuck through the kitchens, KO'd two cooks and then turned to see a guard running towards an alarm. I had already triggered two, so if he made it it was mission over. There was a camera on the door, I was supposed to take the long way around through the vents, but that would have taken too long... anyway, this guy reaches for the alarm just as I see a bottle on the table in the kitchen. I pick it up, throw it at him to get his attention. It worked, but not how I hoped, as I watched it sail over and hit him square in the side of the head, knocking him unconscious.
Also, later in the level I'm meant to be getting picked up in some van, but a security guard is talking to the driver (the courtyard is lit up- I couldn't sneak across). I'd spent all my shockers on other guards, and I was standing on a second floor roof 15 feet away from him. I take a run up, land squarely on his head, knocking him out and triggering the cutscene at the end of the mission... just as well, being as I'd just lost the last bit of health that I had (I actually hit the ground, started to keel over and the CS triggered... best timing EVAR)