When you hit someone using a urinal from the back of their head causing them to "kiss the potty" as their head bounces off the wall. They are typically done in a bar.
"Shorsery-- that guy you potty kissed at the Coleson brought his buddy around this time"
When someone is having a piss at the urinal and you bang their forehead against the wall
Dude was talking shit at the bar so I gave him a potty kiss at the urinal.