sack sludge
The residue that remains on one's ballsack after sweating profusely. Normally indicated by the build up of residue on one's fingernails after scratching one's balls.
Bro, what's this shit on my fingernails?
That's just your sack sludge bro, it happens when your sack gets all nasty
That's just your sack sludge bro, it happens when your sack gets all nasty