Well, wash that crap off to start. Then it's time to disinfect...I'd use hydrogen peroxide or rubbing alcohol. Then slap on some Neosporin and hopefully the cut will heal without any problems. Go see a doctor if the infection gets any worse. And, oh yeah...don't ever rub feces on yourself again. I don't care how many of the cool kids are doing it.

Good luck to you and your scrotum.