The personality disorder that involves lecturing others or constantly explaining things to them as though everything is new to them, even when the other person already understands these things, is called "know-it-all" or "grandiose" personality disorder.
This personality pattern is characterized by a sense of superiority, an inflated self-image, and a need to be seen as exceptionally intelligent or knowledgeable. People with this personality trait often believe that they possess unique insights or expertise that others lack. They tend to dominate conversations, disregard the input of others, and may come across as condescending or arrogant.
It's important to note that the "know-it-all" behavior may not always indicate a diagnosable personality disorder. Some people may simply have strong egos or be excessively confident in their knowledge. However, when these traits significantly impair a person's ability to maintain healthy relationships or function well in various social and professional settings, it may be indicative of a more severe personality disorder.
It's essential to consult with a mental health professional for a proper evaluation and diagnosis if you or someone you know is experiencing persistent difficulties related to interpersonal interactions and self-centered behavior. They can provide appropriate guidance and support to address these challenges effectively.