The student who filled my lab coat pockets with shaved ice from the ice machine while I was carrying a large and heavy piece of equipmentso I had to walk a long way with my pockets full of melting ice,then made good their escape( so they thought), and trotted down the three flights of stairs to leave the building but didnt know I knew the exact moment to release an egg from the balcony to hit them exactly on top of the head as the crossed the lobby, The egg had been "blown out" and the contents replaced with glycerol, (no stain and mess and washed off easily , but the same feel).I will treasure forever the expression on her face as she looked up at me...