Avoidant Personality Disorder
Avoidant personality disorder is characterized by extreme social inhibition (shyness), feelings of inadequacy, and acute sensitivity to actual or perceived rejection. While most people have certainly feelings of insecurity, for people with avoidant personality disorder these feelings are extremely intense and lead to an avoidance of social interaction that negatively impacts their day-to-day life.
1Lenzenweger MF, Lane MC, Loranger AW, Kessler RC (2007). DSM-IV personality disorders in the National Comorbidity Survey Replication. Biological Psychiatry, 62(6), 553-564.