Back when I was in the 6th grade in the mid-80's, our teacher would take us to the Library's media room to watch a slide show on the Galápagos Islands and other science stuff.
The way it worked... there were the slides and there was a tape. And whenever there was a beep on the tape, the person handling the slide machine would advance to the next one.
I loved being the one that did that. And I would usually always get to do it. Except this one time. And I was pissed. The machine had a switch that would let you advance through the slides quickly, so unless you tapped the button ever so slightly, you would advanced two or three slides. So without anyone noticing, I flipped the switch.
My poor classmate kept skipping slides And having to go back. And try to get on the correct slide. Till the teacher told me to get back on the machine. I flipped the switch back to normal speed, and there were no more skipped slides.
So young and so evil.