He knows that in theory but he doesn’t believe that it should be embarrassing because for him and his group it’s normal. He knows how the community views it but he clearly doesn’t agree or he wouldn’t be doing it. He’s 17 so he’s selfish and thinks he rules the world. He can’t imagine that anyone else’s opinion should come in the way of his own, especially if the community who holds that opinion is a community that threw him under the bus.
Also I meant to say that he doesn’t think that his partying SHOULD be embarrassing to you.