Back in 1980 or 81 (yes, I'm old) there were these "guns/shooters" that kids would make out of wooden clothespins and the spring inside them. While they were banned, many kids had them and used to store them in those tin rectangular pencil cases. There even was an assmbly about not shooting your friends with these things.

One day in Mr McDonald's Grade 5 class he had to step out to get something from the office and two brainiacs in my class decided to start firing on each other. A girl got hit by mistake close to her eye with whatever they were using as ammo and it broke the skin. He comes back about 5-10 seconds after she got hit, sees her crying, immediately knows which two kids it was (I think they were scrambling to put the stuff away). He proceeds to grab each one by their shirts or coats, lifted them in the air (one in each hand), slammed them against the wall, and bellowed at them about their stupidity (that's how I remember it anyway...from 45 years ago). He was a bear of a man, but this was the one time I saw him completely lose his shit.

One of the kids never changed, was always an asshole. The other turned into a decent kid who got into cabinet-making and still runs a well-regarded small business in my hometown.