When a friend is using the urinal or peeing in a stall, you yell "Earthquake Test!" and then push them forward while they are peeing.
John was trying to pee and I gave him an earthquake test. Now his pants are all wet.
This is only a test. Had this been an actual earthquake, your stream of pee would wave to and fro and back and forth in front of you.
In the event of an actual Earthquake, you would probably have peed yourself without getting to a urinal first.