When your ballsack is chaffing off skin into the gusset of your underwear. Usually a result of very dry, unmoist skin or plain old filth from a lack of hygiene.
This dry winter air is hell on even my nut sack. I got the worst sackdruff. It was like a mini-blizzard when I dropped my drawers last night.

I haven’t showered for three weeks now. My scrot is so nasty it’s got sackdruff.
by Eaton Holgoode December 18, 2018
Get the Sackdruff mug.