GD was like this at 10 (not directed at me, but mean, rude and horrid to Gran particularly) I suspect it's about growing up, asserting their own power and status and all that sort of thing.
Don't worry too much about why he's doing it, (as long as you've ruled out bullying and witnessing abusive relationships)Getting hung up on why he does it makes you go round in circles, start questioning yourself, and cutting him too much slack when his behaviour is unacceptable, instead of standing firm and consistent in expecting proper treatment of you
I'd draw a line under all the punishments at the moment (give computer back etc, but with a limited time per day) BUT put up a list of a few rules (tell the truth, be polite, tidy up own clothes or whatever). Then make some vouchers with a value (say extra 5 minutes on computer, or 5p pocket money, but keep the unit value very small). If he says don't patronise me, or similar then fine, he doesn't get vouchers he doesn't get the goodies.
Make a point of noticing and rewarding the behaviour you want and award vouchers. This should be the ONLY way that he can get sweets/treats/computer time/you spending time playing or putting yourself out for him or whatever it is he wants. (I also gave vouchers to her brother so they both had same system and same opportunities for treats) I used to sign the backs, after a rather poor attempt at forgery.
There needs to be absolutely zero tolerance of disrespect. Any of the behaviour you describe needs to be met by both of you saying it's not acceptable and sending him out of the room until he's prepared to behave properly. If he's not prepared to do this then he needs a sanction that will hurt(loss of computer etc) but it should never last beyond bedtime so that tomorrow is always a fresh day, If they feel they've got nothing to lose they won't behave
It took about 6 weeks to get her back to being the sweet kid she was before, and has lasted really well. the voucher system isn't in use any more as these things don't last forever, but I would definitely do it again.
Good luck, it will pass, let firm but fair be your mantra, and insist that DH backs you up.