Crow's Nester
Taking a dump in a urinal in a men's bathroom. This term pays homage to the 'upper decker' of yore. Since the urinals are usually mounted higher than other disposal units in the bathroom, it just makes a lot of sense.
Once, at a marathon, a runner came in to take a Trump/Clinton (your choice) and it was all hands on deck. So he saddled a urinal and gave it a good crow's nester.