The personality disorder that involves lecturing others or constantly explaining things as if they are new to the other person, even when the other person already understands, is known as "know-it-all" or "egotistical" behavior. This behavior is not a specific personality disorder recognized in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) but can be associated with certain personality traits or disorders.
One personality disorder that might exhibit such behavior is Narcissistic Personality Disorder (NPD). People with NPD often have an exaggerated sense of self-importance, a need for excessive admiration, and a lack of empathy for others. They may feel entitled to assert their knowledge and superiority over others, even when it is unnecessary or inappropriate. Lecturing and explaining things to others, especially when they already know or understand, can be a way for individuals with NPD to maintain a sense of control and dominance in social interactions.
It's important to note that not everyone who exhibits such behavior has a personality disorder. Some people may have learned this communication style due to various factors, such as upbringing, socialization, or specific life experiences. Additionally, other personality disorders or traits could also contribute to this behavior.
If you or someone you know is struggling with interpersonal relationships or exhibiting problematic behaviors, it's essential to seek professional help from a mental health professional or psychologist. Only a qualified clinician can properly assess and diagnose any potential personality disorder or other mental health concerns and provide appropriate support and treatment.