Oh there are many...!
One of my favourites was when we were having a flobbing competition during break out of the first floor classroom window. It was your's truly's turn and I took the customary preparations and long run up before releasing my effort. It unfortunately was a dud and descended straight down landing in the centre of the bald patch on the art master's head as he was passing below. He was very fast indeed turning the corner and running up the stairs but, fortunately, not quite as fast as we were in vacating the classrom!