When a person has one significantly longer fingernail on one or both hand(s), most often the pinkie nail, which is used for scooping up powder cocaine and snorting it. This is known as doing a bump. The nail becomes the vessel as opposed to needing an item to snort a line of coke through; ie, a straw, rolled up dollar bill, etc...
When someone has at least one abnormally long fingernail (usually the pinky) on each hand. Though it is not usually stated, it is assumed to be a substitution for a straw, rolled-up dollar bill, etc. for snorting cocaine.
Guy 1: Man, I wanna do some blow, but I'm outta straws and cash.
Guy 2: I got ya, scro! That's what my coke nails are for!