Sure you can. Someone points a gun at you, you can shoot. Someone breaks into your home, by law you can shoot in most states. Most laws do not require you to necessarily incur an injury to be threatened. There was another case not too long ago in Florida involving a white hispanic and a black kid where these concepts (Castle Doctrine, Stand Your Ground and straight up self defense) were discussed at length. I would refer you to those threads.
I posted most of those threads and followed it from start to finish and you don’t know what you are talking about.
Point a gun at someone or breaking into their home are acts already committed when you shoot, not things you think they might do, both of which most people would say create a reasonable fear of harm.
You can’t shoot them if the gun is on the car seat and you think they might point it at you, nor if they are parked in front of your house and you think they might be about to break in.
So the question about the popcorn throwing, is whether that creates a reasonable fear of injury that justifies deadly force.