It feels so good when you run your fingernails over my back.
- C'est tellement bon quand tu fais courir tes ongles sur mon dos.
You have dirt under your fingernails.
- Tu as de la crasse sous les ongles.
He managed to cure himself of his habit of nibbling his nails.
- Il a réussi à se guérir de son habitude de se ronger les ongles.
Don't bite your nails.
- Ne ronge pas tes ongles.