After a man ejaculates he goes and takes a piss to rinse out the cum from his urethra.
The little pain you get peeing after you ejaculate. Thats the cum washing out of your dick.
Guy #1 Damn it hurt like shit when I pissed this morning
Guy #2 You masturbated last night before you went to bed didn't you?
Guy #1 Yes I did! How did you know?
Guy #2 Damn dude you got to "Piss Rinse" after you jack off so this shit doesn't happen you dumb fuck.