Actually, the first thing you should do is walk away. If, as in this video, the bastard doesn't let you go, then you beat the fuck out of him, take his gun for your own protection, and make a citizens arrest.
Yeah. more correclty I meant that if someone has threatened you with lethal force, and the situation unfolds such that you are successfully defending yourself, don't stop until you are pretty damn certain the threat has ceased existing.
Look out for the punk gang banger to come back and shoot you in the back
raz-00
Guy pulls a gun on you for no reason, you should beat him till he stops moving and is no longer a threat.