Alright, I'll join in. I taught high school physics for 10 years and during my first year, they had just "renovated" my classroom. They put in a bunch of computers and caged off the lathe, drill press, and whatnot but put just a bunch of random stuff in there too. Included in that list was a glass Hoffman electrolysis apparatus and a bunch of 12V lantern batteries. You shouldn't leave stuff like that just lying around for me to find.
Not that it had anything to do with what I was teaching at the time (kinematics or something, but I decided to hook up two of the batteries in series and ran it for a while. It produced quite a few bubbles and filled up the hydrogen side pretty quickly. I then showed my class what happens when you put a burning splint at each of the two valves (O2, H2). They thought the 12" tall flame on the hydrogen side was pretty impressive.
What I DIDN'T show them was when I hooked up eight batteries in series (96V DC) during my off period, switched the polarities halfway through the process (producing O2 and H2 in the same container), and then held the splint to the valve and opened it. Luckily the electrodes were attached to rubber stoppers because they absolutely blew out the bottom like a gunshot rather than the glass exploding into my face. There was water all over the batteries (but didn't short them out somehow) and the aluminum electrodes that had been in the glass chambers had completely vaporized.
When I told my students the story, they asked why I hadn't waited for their class period to do that