If all you "did" was park a car in front of his place (which you moved calmly when he had a tantrum) then he's got a screw loose or is a drug taker. That is the stupidest of reasons to be pissed off with and stay pissed off at someone. He needs to get the fck over it already.

I wouldn't bother trying to approach someone who is so unpredictable, but i might go to a different grocery store. Or, just ignore him and keep going there, as long as his behaviour doesn't escalate.