To coat the floor, walls, and sometimes ceiling of a room with urine. Can be done either intentionally or unintentionally. Noun form of gurnicking
Man 1: Why does it smell like dried piss in here?
Man 2: Mike came in and decided to gurnick the bathroom last night.
Man 1: They really should put a light in the bathroom in this bus.
Man 2: Don't tell me you gurnicked it.
Man 1: Well, I can't tell for sure, there wasn't a light!
Man 2: You little shit!