The build up of dirt and grease under the nails resulting from the inability to clean oneself properly during a weekend coke binge. Usually noticed at 8am Monday morning after two hours sleep and no time to have a shower before work.
An experienced professional will have a 99p nail brush purchased from Tesco on his person at all times.
"Jesus Christ, who has bled over the note? Fuck that, look at your fucking coke nails!!"
"Oh sweet Nathan has taken posted another selfie - dude, check out his coke nails"
"Can't believe he tried to finger me with his coke nails"