The act of taking a leak (urinating) then not washing your hands and just leaving.
Mostly performed by people in airports who are in a hurry to catch a flight. Or those who are just to lazy to wash their hands.
(Both men and women can perform a Leak & Run)
Dude #1: Dude, that guy jus took a piss and didn't wash his hands.
Dude #2: Man, that's nasty, he jus did a leak & run.
Dude #1: Must've been late to his flight.