Clinical term for compulsive nose picking.
For a penetrating study into the subject, I recommend delving into the article "A Preliminary Survey of Rhinotillexomania in an Adolescent Sample"1 by Chittaranjan Andrade, M.D., and B. S. Srihari, M.B.B.S.. This in-depth survey of nose-picking behaviour in 200 adolescents from 4 urban schools in Bangalore, India (Doctor Andrade is on the faculty of the Department of Psychopharmacology, National Institute of Mental Health and Neurosciences, Bangalore) has received the "thumbs up" from the committee of the Ig Nobel Prize, and has become the just winner of the 2001 Ig Nobel Prize for Public Health.
1 Journal of Clinical Psychiatry, vol. 62, no. 6, June 2001, pp. 426-31. Abstract available online at http://www.psychiatrist.com/abstracts/200106/ab060104.htm.