They are made from streched acrylic, there are (typically) two structural and one protective pane. Structural design is "waiting fail safe", meaning the outer pane takes 100% of the pressurisation. The middle pane has a vent hole, so it does not carry loads, unless the outer pane has failed. In that case there is a minor oir leak through the vent hole. The inner pane is purely protective and decorative. Streched acrylic is qute a robust material, hard to destroy by a passenger without special "tools". Especially as you first have to destroy the decorative pane, then the unloaded middle pane (so pressure will not "assist" you), and then you can do real damage.
I am quite sure it never happened (except in the Goldfinger movie)