I think I've done the hammer slammer on my bro. We both collided in midair, him with the hammer, me with an assault rifle. I already lowered his armour a bit with my rifle and we both went in for a melee. He hit me and I lost my shield but I survived (oddly enough, considering he hit me right on) and I hit him and he went flying up into the air and died.
And it's all on replay.
