How do you handle unprovoked hostility?

I parked in a parking lot today and it wasn’t the best parking job ever but I was within the lines and in a hurry. I didn’t straighten out the car. When I came back, there was a note on my windshield saying, “You park like an asshole. Have a good day dickface.” There was a car parked next to me. My guess is that someone in a big SUV had wanted to get into the next spot and couldn’t, was angry and so the note.

No immediate threat of course. I tore up the note and threw it away but it leaves a bad taste in my mouth. How do you handle the feelings of an “encounter” like this? What provokes someone to be so hostile to a stranger?