bite your nails/fingernails
bite (one's) nails
1. Literally, to chew on one's fingernails and shorten them. I wish I didn't bite my nails, but it's been such a hard habit to try to break. My sister gets regular manicures to keep from biting her nails.
2. To nervously await something. I've been biting my nails ever since I submitted my application for my first-choice college.