If you think busting a car's window is easy, just ask this guy how the brick method is working for him:
There is a reason those car safety kits come with a specialized hammer to break the glass in case of emergency. The trick is to direct all the force through a very small spot. If you hit it with a blunt object, like a regular hammer or brick, it is likely to just bounce off. And if your tool has enough of a focused point, it doesn't actually take that much force.
Cleetus McFarland may have to sacrifice a perfectly good spark plug to try this experiment, but it is so worth it. After breaking apart the spark plug, they pull off a chunk of the ceramic insulation to see if it can break the glass.
The tiny ceramic shard works perfectly to explode those windows. It has to hit just right, so the extremely sharp edge transfers the small amount of energy just so.
While this isn't the most practical method to bust out the glass in an emergency, it is a pretty cool party trick. As long as you are only using it on the spare windows you have lying around and not on anyone's car.