Driver = wrong for making a no-look 3 lane change and giving the finger to anyone in her way
OP = wrong for spitting on someone

Not that I don't have a temper when it comes to drivers doing stupid things, but I don't spit on people (any more... way back when, though.) I'll yell, I'll smack their hood/roof/trunk, but if the window's open my personal fave is a quick spritz from the water bottle.
Spitting at them may have the "Ewwww" factor, but nothing wakes a driver up quicker than a blast of ice water to the side of their head.

As for the internet tough guy who would hold someone at gunpoint until the police arrive... I don't think you've thought your cunning plan all the way through.
- Are you prepared to deal with the consequences of holding an unarmed person at gunpoint? The police don't typically go after the guy on the "wrong end" of the gun when they arrive on the scene.
- Are you seriously suggesting that you would shoot the offending individual if they attempted to leave the scene? If so, seek out some anger management sessions and please, get rid of all your firearms.