The person in question takes a wet wash rag or wad of napkins, sometimes soaps them slightly, then washes the under arms, neck and private areas vigorously.
Sheila: "Don't worry, run to the bathroom and take you a Slut Bath. You'll be fine."
"Wo, you had a slut bath didn't you?"
Person A: That girl looks insanely slutty.
Person B: Someone took a long slut bath.