pickus digitus
The fairly common act exhibited by someone when nervous, worried or scared about a situation. Symptoms involve the removal of skin from around the nail area of a finger(s) - either using fingers or teeth.
Joey: I don't know wot you're worried about man, I mean you studied hard for that exam - I don't get why you need to pickus digitus.
Rick: Yeah you're right, but it's this bad habit I got.
Rick: Yeah you're right, but it's this bad habit I got.