Black shit that you pick off your balls when they itch. It's often attached to little pubic hairs.
My balls are covered in ballsack black.
it’s black it’s big AND it’s a ball sack merges with a kneecap
me: HEY GUESS WHAT
slade: what?
me: I GOT A BIG BLACK BALLSACK KNEECAP
slade: oh damn i’m jealous