The result from the tendancy of liquid traveling at a high enough rate of speed to rebound off of a hard, non-absorbant surface (like the back of a urinal) and wet the person standing at the point of origination.

Specifically, this is when, while taking a piss, some of the urine splashes back onto your pant leg. Especially common if you are, like me, taller than the average person. A combination of low hanging urinal and a package about six inches higher than where is ergonomically average just exacerbates the problem.

See The world is run by midgets