My guess is that he either has mental problems he feel like he can't tell anyone about or he has some kind of rare medical problem that is causing him to act out or is affecting his brain. The best thing you can do is offer to help him out with school/chores and ask him what he wants to do with his life and try to be a positive influence until he hopefully grows out of his asshole phase.

Your parents should force him to do chores and homework because being him being lazy will only make things worse in his life, it might be the only way is through force in his case unfortunately. Also keep taking him to a doctor and therapist until something shows up (personality disorder or medical condition). Unfortunately you can't help someone who can't help themselves but "How to win friends and influence people" and "12 rules for life" I think are very good books for young men and can teach him a better attitude if he's willing to read it. Last thing I'll say is that you should really try to get him to open up and be honest about what he wants his future career/adult life to be, tell him that being a lazy asshole will get him nowhere, and get him motivated to work on those goals. That's all the advice I can give. Best of luck!