RED NAIL Share definition Flag Its when someone sticks there fattest finger up there ass, which cuts of the serculation to the nail which causes it to turn red. My teacher did a red nail to me and kept it in for so long that she had to go to the E.R. RED NAIL by The finger master March 14, 2004 0 0 Get merch Get the RED NAIL mug. Buy Now — $32.95 See more merch