Good evening and thank you for the opportunity to help in answering your question. Based on the information you've provided it sounds as though your cousin is engaging in a form of defense measure secondary to his actual reality. It's often used by individuals who are emotionally immature as well as having significant insecurities. It's likely that he shares this false information with individuals who would likely not "check up" on his lies. He tries to inflate himself in order to cope with his actual reality.
It's not a psychosis given that he is consciously aware that he is telling lies rather than this being a delusional thought...so it's more neurotic behavior than anything else.
In short, he's embarrassed by his reality therefore he inflates himself to a level that he actually wants to be in. A lot of people who do this actually believe that they will be there one day so they justify their lies to themselves this way. By confronting him he will likely get immediately defensive and say that he is "just having fun" and will continue to engage in this behavior regardless of who knows the truth.
I hope that this helps to answer your question and shed some light on his behavior.
Please let me know if you have any further questions that I can help in answering for you. I want to be certain that I have answered your question completely and thoroughly.If you feel that I've answered your question to your satisfaction then I would greatly appreciate your clicking the ACCEPT button thereby giving me credit for the answer and suggestions I've provided to you. I hope this finds you well and look forward to your response.
You are indeed welcome for the answer. As for neurosis vs immaturity. My best impression based on what you have mentioned...as well as other individuals I've come across in my practice...it likely started as a result of immaturity and given the response he continued to receive it undoubtedly developed into a neurosis which would require professional intervention in order to help him work through it at this point. After a while of telling ourselves something....it can become so ingrained that there exists a significant exertion of energy in order to keep up with the lies.
I hope that helps to further answer your question. Please let me know if you have any further questions. If you're satisfied with the answer I'd appreciate your clicking the ACCEPT button. I hope this finds you well.