Experiment: a piece of candle easily breaks something that a hammer cannot break
You will be surprised to know how you can break almost any tempered glass.
There may be situations in life when it is necessary to break tempered glass. Many of them are very strong, so this can only be done with a hammer or sledgehammer, but not with a stone.
However, they are almost 100% likely to break from a light ceramic spark plug fragment.
Glass breaking process
You need to take an unnecessary spark plug and crack its ceramic insulator with a hammer.
From the resulting fragments, you must select the largest shard with at least one sharp edge.
The ceramic fragment of the insulator must be thrown into the glass, like a dart, with the tip first.
Although it is lightweight, its hardness and point pressure will immediately break it.
Such a fragment can even cope with car glass, of course, if it is not triplex, which, when broken, will not fly into fragments.