This occurs when there is clogging in the urethra due to the remaining residue of ejaculation, either from masturbation or copulation. The clogging results in your urine shooting in any direction but the direction you want it to go. Your legs, shirt, toilet seat, sink, floor, and even face will become drenched in a yellow spray.
It is always a good idea to sit on your toilet seat after ejaculation to prevent split piss.
After you dump your spunk and wait a little while your one-eyed warrior sometimes gets it's eye stuck shut and when you hang a rat you piss in two directions at once, neither of which was your primary target. Usually involves a leg or a favorite shoe. If it involves a face you are either R. Kelly or fucked up or both...
"No-o-o-o, a doberman didn't hump my leg. I went splitpissin' after yankin' my yoda to the latest edition of FHM. There's a couple of pages in there ain't nobody ever gonna yank apart..."