An old woman was at the hospital due to bouts of explosive diarrhea.  While sleeping, she soiled her sheets terribly.  Being embarrassed beyond all rational though, she snatched up the sheets and threw them out of the window.

Below a drunk just happened by that very window.  The soiled sheets fell on his head and he began to thrash and curse and punch at the air.  The sheets landed in a pile at his feet.

Seeing all of this, a security guard approached the drunk.  Barely able to control his laugher, he asks the poor inebriate just what he thought he was doing.  The drunk slurs, "I think I just beat the shit out of a ghost!"