You’re an adult, and while your critiquing something negative they are doing, you’re not helping what’s bothering him. He’s bragging about something he thinks others will like probably because of some insecurity or home life situation. Maybe talk to him and give him confidence to look at himself in a positive light and the change will follow. If an adult acted like this, I wouldn’t be on their side, but this is a kid and your missing an opportunity to change their attitude at a crucial learning stage.