A stain left on clothing, bed sheets, or other types of material. Contains piss, night cum, sweat, shit, or a combination of those. It usually incorporates a thick, pungent stick and the residue proves to be unwashable, thus making it the worst of all stains.
The origins of the phrase 'Billy-stain' are from one Billy Boggs, an unclean middle-aged man who wallows in his own filth every morning.
Chunky: "Wake up, Billy...Wake up! It's three in the afternoon!"
Webbie: "Look, he's covered in Billy-stains! Nast!"