Hi, thanks for the query. Any behavior which causes significant distress or impairment in a person s social, occupational, personal domains is usually characterized as a disorder. Similarly if a particular behavior (ripping toe nails) is causing significant distress to close ones, family members can also be termed as a disorder. Based on this account; do you feel that your friend is getting into trouble because of repetitive ripping off toenails? are there any other repetitive behaviors like excessive need for cleanliness, orderliness, symmetry, any excessive religious beliefs, counting numbers, things or activities like repetitive hair pulling?? Do revert back with these answers. We may consider possibility of obsessive compulsive disorder (OCD) or impulse control disorder spectrum based on your answers to my queries. Once confirmed, we shall proceed to treat this behavior/set of problem behaviors accordingly. Hope this helps