The act of putting on slippers in anticipation of being on the toilet for a long time, in order to be more comfortable while taking a time-consuming dump.
He ate a lot of Chinese food last night, so he's probably slipper pooping right now. Might as well be comfortable, right?
When you step in such an enormous pile that it squishes up through your toes and wraps around your foot thus forming the poop slipper
Bill was just having a nice barefooted walk in the grass and stepped in such a monster pile of dogshit he got a poop slipper