You're implying the drunk driver has 'intent' to do you harm. I can't be certain, but I would guess MOST people who drink and drive do so with the aim to NOT hit anyone or do harm to anyone, as that would effect them as well. Where as with your example, someone aiming a gun at my head is a 'direct threat' against my well being. Therefore I would have the right to get the gun out of my face using whatever methods I saw fit.