Answer: Narcissism is characterised by an inflated self-image which is commonly found in teenagers due to the high value they assign to talent, beauty and popularity among their peers. In this case, we're talking about an adult children who has narcissistic personality disorder so it can't be considered as a normal evolutive behavior. In a typical therapy, a professional would pay attention to certain behavior/reactions on the patient like body language and also statements typically associated to this personality disorder. The avoidance of self-criticism (not admitting mistakes), behaving childishly when things don't go their way, among others, would be common signs in this adult child.