When you leave the toilet lid down completely and sit with your bare butt cheeks flat down on top. Then when you defecate, the forcibly expulsion just slip slides you all around and ends you up gliding off the front as you proceed to land on the floor in a big pile of your own mess.
Johnny: Dude, the bathroom is all covered in feces, what happened?
Dude: Couldn't help but perform a North Carolina Mudslide after I got all shitfaced at the club last night.
Johnny: And I thought an upper decker was gross. You're on another level dude.