maybe not the funniest, but certainly the scariest.... During stretching I noticed my first grey chest hair. Nearly cried.
Many years ago, whilst waiting in the corridor of a building where we were to be graded by Sensei Tomiyama, a nearby student knocked over his bottle of Tizer. The puddle of Tizer expanded and headed over to where I sat. I suddenly felt my extremities getting cold and wet. On standing up and inspecting the damage I saw a nice big orange patch on my freshly laundered white gi bottoms.
When trying to explain the 'up turn' of the pelvis in Tensho, I asked one of my colleagues to 'test my stance' with swift Kin Geri from the rear....I found out the hard way that my stance wasn't very good. I had to carry on teaching the class through the agony....actually, thinking about it...it wasn't very funny!