In my state, it applies to vehicles as well, it's kind of a cross between the stand your ground/make my day laws and castle doctrine. Second paragraph of this will prove it:
Walker signs 'castle doctrine' bill, other measures - JSOnline
For the record I was giving a worst-case scenario. I'm typically level head headed an my fear of of actually using my weapon would stay my hand but that cannot be said for everyone when adrenaline is pumping. That's what I wanted to point out. Assuming no weapon I'd take a picture of the guy and his license plates with my phone then call the cops (as I've done before). If he was hitting the glass so hard it started cracking, then I'd have a reasonable fear for safety enough to draw my weapon.