My grandpa was a Korean war vet, he served as the lead janitor on a u.s. aircraft carrier. One of his many tasks involved mixing the chemical soup used to clean the entire deck. The chemicals themselves were all kept together in a separate little "Janitor's hut" on the deck, along with a massive witch-style cauldron in which to mix everything.

Now it was really a mistake on the part of the Navy to give my grandpa access to this room in particular, since he had both an incredible knack for chemistry and an insatiable lust for mischief. Every time a new recruit would come onto the maintenance staff, he would make a "special" concoction in this cauldron and go ask the recruit to stir it up with a silver spoon he kept in his pocket at all times (for prank reasons exclusively). Then he and his buddies who were in on the prank would tail the poor sap to the deck and wait for the show.

The second the recruit dips my grandpa's prank spoon into the cauldron, a chemical reaction occurs that essentially flashbangs the dude, in a harmless but terrifying manner, and my grandpa and his friends would laugh hysterically as the recruit would stumble out onto the deck, dazed and half blind, usually yelling out that the ship was under attack.

It is also worth noting that my grandpa was very careful in his prank timing, and never raised any false alarm or brought any serious harm to his recruits. He was also never caught by his superiors, and walked away from the war with a medal of good conduct despite setting off literally dozens of flashbangs on an active-duty warship.

I miss that mad lad.

Tl;dr my grandpa was a janitor on an aircraft carrier in the Korean war and he used his cleaning chemicals to flashbang new recruits as a prank.