If I splash water on the sink, I'll use a paper towel and dab it up. But so often one is greeted by the sight of an overflowing toilet or sink which has been either abandoned by its last user, or stuffed with towels and toilet paper in an attempt to stop it. We don't have to clean it up. No one we know has to clean it up. It's our one chance to really do something marginally destructive to screw up some poor sod's day.
Someone does have to clean that mes up.
But since we'll never know him, we all feel perfectly justified in walking away from the overflowing urinal. We'll just step blithely over the murky pool of fluid on the floor, and be on our way. If we destroy a toilet with the effort of our bowels, we'll just walk away - flushing is the next guy's problem. No courtesy whatsoever. Public restrooms epitomize everything I loathe about modern culture.