dirk stain
A dirk is a cigarette. A dirk stain is the yellowing of the fingers due to the dirk smoke.
Katie: "ew man I need to quit smoking, these dirk stains are seriously gross!"
Jon: "cut up a raw potato and rub it on your fingers. I guarantee it'll take away your dirk stains"
Jon: "cut up a raw potato and rub it on your fingers. I guarantee it'll take away your dirk stains"