Used to describe a bathroom that was once the ideal bathroom in a location, but has become repulsive due to the amount of excrement endured by it.
"Dude, that M Building bathroom used to be so clean, but it's so overshat now."
You do oversleep, but what about when you really have to take a dump and you miss your buss.
Child: Dad, i overshat. Can you drive me to school.
To a friend; I'll be 15 minutes late. I overshat.