Junior year, my buddy and his friends are making little grenades. They had just found the anarchist's cookbook and were goofing off. No intention of hurting anyone just high schoolers being idiots. Well one of them thought it would be absolutely hilarious to take the gas and some of the unfinished tennis ball bomb things and stuff them in his backpack and leave it under a small staircase on the outside of the campus that few people use.

Well a teacher noticed that backpack. And the next thing you know the campus is in lockdown and the police are searching every room and we all have to come out of our classrooms one at a time as the police search un individually. They had dogs, metal detectors. everything.

Friend realizes they have his backpack and is scared and confused. Police didn't know who it belonged to they confiscated it, nothing came of it other than a nickname for our friend. And years of jokes.

A year later we are graduating and friend who's backpack it was is a grade A student liked by everyone and on his way to being a great engineer.

TL;DR Buddies are making pseudo explosives. Friend thinks it'd be hilarious to stuff their bag full of unfinished ones and leave it under staircase. Police come and search everyone. Nothing happened.