What is the meaning of Elon Musk's tweet about people with 'Ph.D.' in their social media names, and what tone does he use?

The tweet by Elon Musk expresses his opinion that people who include "Ph.D." (Doctor of Philosophy, a high academic degree) in their social media names are pompous (arrogant or self-important). He uses a derogatory and offensive term to imply that such an action is a sign of arrogance and a lack of intelligence.