The time when someone stands in front of a row of portable toilets or "Johns" and must gamble on which one seems the most sanitary. This is much like a "lottery" which is why it is referred to as a "Portable Potty Lotty".
Mary really had to play the Portable Potty Lotty when she approached the concerts portable toilets. She ended up winning by selecting the one toilet that had not been defecated in.

Gary lost the Portable Potty Lotty because as he stepped into his portable toilet he released a loud shriek. He exited with poo all over his pants and shoes. Poor gary, maybe next time you'll win the Portable Potty Lotty.
by The True Shannigan August 18, 2009
Get the Portable Potty Lotty mug.