Green’s Dictionary of Slang

a piece of excrement adhering to the anal hairs.

1997		Roger’s Profanisaurus in Viz 87 Dec. n.p.: winnit n. Kling-on; dangleberry (qv); brown room hangers on.
2001		OnLine Dict. of Playground Sl. 🌐 winnets n. small pieces of excreta (and other material) that cling to the hair around the buttocks, and into the buttock cleft.