Two are tied.
Back in the Halo 3 beta, when the trip mine was all-powerful, on Valhalla, I threw it down where one of the mancannons land. I move a bit away and a warthog comes barreling around the cliffside, fully packed, and it's gonna kill me. Next thing I know someone lands on the trip mine, he dies, the warthog blows up, and I get four kills due to that one accident.
Bad Company 2, I'm sniping because every other weapon is so glitched I could furking kill the designers, I look out a window and see a guy aiming a rocket at me. He fires the thing, I try and shoot it and snipe him in the face. I step away from the window and the rocket crashes through that window and out another window on the wall beside it. That was a great day...