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Unspoken but widely understood rule regarding selecting a public urinal, specifically if there are five urinals to choose from. If all are unoccupied you choose the one on the far left (1). If this one is occupied you choose the far right one (5). If both are occupied you choose the center one (3). The object is to maximize the space between yourself and anybody else who currently has their shlong out.
urinator 1) "Hey buddy, one five three rule. Scoot over."

*scoots over*

urinator 2) "Sorry, wasn't thinking"
by skid mark vz March 06, 2008