speaking of the law, i think there's a limit to which you can
exercise your right of self defence on your own property, even if
it means resorting to lethal force to effect that defence. if you
can prove that whatever hell you gave the person was necessary in
preventing further damage to be done to your car, heck, you could
even get away with murdering the prick/faggot who's dausing damage
to your car. so i say, beat the hell outta them, just make sure you
can justify the beating. 
