A crusty substance coming off of some guy's balls. This is an advanced stage of crotch rot. It mostly comes from not showering, not cleaning your balls or wearing the same boxers/tighty whities for weeks, even months.
Guy: What the hell is all that nasty crusty stuff coming out of that guy's pant leg?
Other Guy: Aww dude... he has a serious condition of ball crust. I bet his boxers have fused with his scrotum by now considering the output of the crust.
Towelie: Wanna go get high?