Here's my two cents and then some:

Think about what he's bragging about and to who. I mean really, does he think you're going to be impressed by all that? The kicker is what else does he have to brag about or be proud of? That may be it. He'd rather look bad than stupid or just doesn't care. Either way take him fishing but as kb said with clear expectations. Don't read the kid the riot act, just be clear, consistent, and firm. Ignore negative behavior (little things) as much as you can and take him fishing. He needs it.