Three spring to mind (sorry for long post)
1 The way my primary school worked was that everyone sat on the floor apart from year 6, who got to sit on benches (lucky sods). Unfortunately that meant the rest of us were so tightly packed that you couldn't really adjust your seating position once you'd sat down. Cue year 5 me realising just as I was due to get up to leave the hall at the end of assembly that I had developed a rather bad case of pins and needles in one of my legs, causing me to trip over and practically land in the lap of the boy I'd fancied for about 3 years. However, this pales in comparison compared to what came next-a year 6 girl who was in my violin class was convinced that the best way of curing the pins and needles was giving me the heimlich manoeuvre. Just outside the doors to the hall. As the rest of the school filed past.

2) Fast forward to year 7, where my new school gives our year the task of putting together a few sketches on "fairness" to make an assembly. My friends and I devise a sketch resembling a G8 summit of sorts, where representatives of a 3rd world country were deemed irrelevant, but Camilla Parker Bowles was given enough money for a new dress. I was Vladimir Putin. Curtain up on President Bush dancing on a table with Tony Blair to Touch My Fire by Javine.

3) In my secondary school the headmistress stood on the stage behind a table with the stage curtains closed behind her. On one fateful Muck-Up Day, the then year 13s hid behind the curtain and, during hymns, stuck cardboard cutouts on sticks of the headmistress's face out from the sides of the curtains and waved them about. After about 20 seconds the head stopped the hymn and shouted at them to come out from behind the curtain, at which point they all rather sheepishly trooped off the stage. We weren't allowed a muck-up day after that year.
(aedowin, Fri 14 Jun 2013, 18:06, Reply)