Objectionable 8 year old

[Missandhit]

I’m about to lose my shit!!
I have 3 DC. The DS8 is an absolute nightmare unless he’s on some sort of device. He was being assessed for ADD in school but obviously nothing has happened with that for some time now.
His attitude stinks. He’s so entitled. I tell him off and he just stands there with a smirk and says ‘what are you going to do about it?!’ He’s the same with his dad too. We’re at our wits end. I’ve actually locked him in his room because he was being mean to the dog to spite me, and he’s threatening to jump out of the window(bungalow, don’t panic!) and said when be gets out, he’s going to kill me. Nice!
I’ve unplugged the WiFi now so there’s no chance he’s going back on that any time soon.
This has progressively got worse throughout lockdown but has always been an issue. Youngest DC5 is clocking on to this behaviour and has started showing similar behaviour and copying him.
Help me. Please. Before I up sticks and move out! He’s making family life very unpleasant

have a read of this older thread on a similar topic
www.mumsnet.com/Talk/behaviour_development/1544002-dont-know-what-to-about-my-8year-old-daughters-attitude

I wouldn't be giving back his device any time soon, until his attitude changes. Does he get pocket money? I would say he loses, say, a pound every time his attitude is bad, and he can earn this back through good behaviour, doing chores when asked etc.

He doesn’t get pocket money yet, for this very reason. He’d be in debt by the end of the first day!

It might be worth introducing pocket money? I know it might seem counter productive right now, but it might give him something to work towards? Put up a chart in the kitchen showing his loss/gain each day. You could start with £4.50 at the start of the week, and he has to keep it rather than earn it. Going into debt for the first week or so might show him that his actions mean he is going to lose something. Make it clear he can spend his pocket money on whatever he likes, write what he is saving for (magazine, sweets etc) at the bottom of his chart so he is reminded.

Up up up up his exercise. Get him out for lots of bike rides. Kick a ball with him. Do GoNoodle on YouTube. Anything to get him moving. Try for 3 hours a day being active.