I have a great moment from Bad Company 2.
Friend is behind enemy lines. He's being surrounded on several sides by multiple enemies. I spawn as a Medic with a LMG beside him and he tries to make a break for it. He doesn't make it three feet from the doorway. Then over his killcam he sees three enemies waiting. Thinking that the enemy is dead, each pause for a moment to either assess what to do next or reload. All of a sudden, all three turn and look over to the door and are mowed down by machine gun fire. What my friend didn't see is my running out of the door, and blindfiring at them, killing each in seconds. The machine gun is one with 200 rounds, and I proceed to run around the enemy base, not even aiming, but instead simply holding down the trigger while everything in front of me gets shredded. My friend is now watching me via the spawn cam, and is in utter shock as he watches me literally run through the middle of the base firing my machine gun from the hip, hitting people left right and center, as some of the defenders break from behind their cover, and instead of trying to return fire, try to run from the psychotic machine gunner destroying them. All this is happening, while over the mic I start to scream such memorable phrases as 'No survivors!', 'I take NO prisoners!' and 'You're all dead! All of you are dead!'. The machine gun finally empties, only for me to switch to my pistol as I round a corner and shoot the last one in the head. In total at least 8 people died from me breaking cover and going Rambo on them. I was finally brought down when the few survivors left caught me with no ammo in any of my weapons. I went to the spawn screen to see my friend still sitting there, neglecting to have spawned, and instead chosen to have sat silently and watched. He had no idea how to react to what he just saw. I immediatly snapped back to normal and cursed the fact I had died. We still laugh about that moment.