Similar to how dogs tag a tree or fire hydrant....
in humans, it's an act of vandalism where someone (primarily males) will urinate all over a bathroom.
Doorknob, sink, toilet, paper products... EVERYTHING!!! And it's super gross, bc the staff of the establishment has to clean it up.
That dude was so pissed he didn't get a discount on his nachos that he tried tagging the bathroom.... there's piss everywhere!