Why are wash pans dropped on a character's head? I've been watching anime for a long time and I still don't understand what it means when a wash pan falls from the sky onto a character's head.  I've seen it recently in Rosario+Vampire when the witch summons a wash pan over another character's head.

What does it mean or represent?
I imagine this is somehow related to the common schoolprank of placing basins/buckets of water on top of door frames and waiting for people to come in and get soaked



As is mentioned in @Vogel612's link, it's sortof the Eastern equivilant of an anvil being dropped on someone's head. A bit more realistic perhaps though.