As someone pointed out earlier, I think you are being hypocritical here. Throwing rocks is not "intolerably dangerous" unless by rocks you mean boulders. It is being intentionally destructive of property - by no means acceptable but not dangerous in any way. The worst you get as a victim is a ding in your car or a crack on your windshield. Would that piss me off? Sure. Does that merit attempted homicide, IMO no. Someone keying your car is a decent analogy to the crime here. No self defense required.
Where your hypocrisy comes into play is the response. Shooting someone with a crossbow is attempted murder same as if a gun was used. If you were to be consistent with your earlier postings, you would defend the right of the teenager to defend himself in accordance with his second amendment rights. I would have expected you to respond by saying that the teen should have pulled a firearm and "defended" himself by drawing down on his attacker. Instead, inexplicably, you are suddently siding with the aggressor and against the one who needed to defend himself.
In some ways, this is the same argument you and I have circled around before. I don't deny that the second amendment allows citizens to own firearms, but I see an armed public as much more risky than an unarmed public simply because of cases like this one (and numerous others I've posted) where one party can claim they feel "threatened" and therefore justified in using lethal force in "self defense". If you think that throwing rocks calls for "JUSTIFIED vengeance" and that includes the use of firearms then all your talk of self defense is really just window dressing. There is no self defense in this case. Your term - vengeance - is right on the money. Is that why people want to carry firearms?