This is the cousin of the dingleberry
, this happens after masturbation. It is when a globule of your jizz gets onto your cock bush and you forget about it. Later, it dries up into a ball and can go unnoticed for a while, unless you take a shower.
Zakk: Dude, at camp, I rubbed off some knuckle children and got a nasty farkleberry.
Henry: ohh god, don't you guys only have showers, like, once a week?
Zakk: Yeah it was disgusting.