Oh I remember one.
When I was in my Business studies exam, we took it in the sports hall (they were too poor to have two halls, so they stuck us in the really inconvenient sports hall).
Above the sports hall was a gym with a window overlooking the sports hall. Someone was on a cross trainer, which faces the window. All the way through my exam, there was one of the music teachers bobbing up and down on the cross trainer. It was very distracting, and I kept looking up and once he waved and winked.
It was quite creepy really.