to bite one's nails
Stop biting your nails.
Ela tem o costume de roer as unhas.
She has a habit of biting her nails.
Você precisa se livrar do hábito de roer as unhas.
You need to break the habit of biting your nails.
Eu tenho o mau hábito de roer as unhas.
I have a bad habit of biting my nails.