As the car gets warm, the snow at the bottom melts. Then the idiot parks it to do his groceries or whatever so it cools back down and freezes into a 2 inch thick block of ice. Then they drive on the highway. That block of ice breaks free, flies up in the air, catches in the wind while tumbling which gives it an unpredictable trajectory and smashes the windshield of a car that was unfortunate enough to be further back at that time.

I know because it happened to me. Had to get a windshield replaced in the middle of a road trip. The dipshit who caused it didn't even realize what happened and kept driving. The police should absolutely crack down on this instead of all the other petty bullshit they tend to harass people over.