18-year male flat affect, odd behaviour. Diagnosis ?

Traits of schizoid personality disorder include emotional coldness, lack of pleasure from activities, limited capacity to express feelings towards others, apparent indifference to praise or criticism, little interest in sexual experiences, preference for solitary activities, excessive preoccupation with fantasy and introspection, lack of close friends, and marked insensitivity to prevailing social norms and conventions. Eliminating the other options, option A: Hysteris/ Dissociative disorder have good reactivity of mood. option B: Schizophrenia can have flat affect, but halluciantion, delusions, thought abnormality or made phenomenon should be present to reach the diagnosis. option C: Depression does not have flat affect. Ref: A Sho Textbook of Psychiatry, Niraj Ahuja, 7th Edition, pg. no. 114