"Yeah," you reply, "we should probably end this. You ready?"
"Yep," he replies. With that, you're both mobile...or as mobile as two badly wounded people can be. He fires another shot, killing a pedestrian. You fire one, toppling a building. He fires another, exploding a row of cars. The battle continues as such until you each have only a single bullet left. If you can hit with this shot, you win. He has the same idea. Both of you are frozen in place, guns leveled at each other's chest. You fire. He fires. You die. You (plural) die.