Paulo Coelho. On the banks of the river Piedra I sat down and wept (№ 95754)

It is a ritual. That it's forbidden. The glasses do not break it intentionally. When we sit in the restaurant or at home, we try not to place glasses by the edge of the table. Our world requires us to be sure that the glasses fell on the floor.
A break in the awkwardness and I unfortunately see nothing special happened. "Don't worry," the waiter says, and I have never in my life seen a broken glass put in the bill. Breaking glasses is a common thing, it happens, and doesn't harm anybody - neither we nor the restaurant, nor the middle.