How can he be so rude to his mom😱 I could never tell my mother to shut up

He is still a kid, a lot of kids rebel like that towards parents.

When I was a kid I never talked to my parents like this and neither do my younger siblings

Well I did

Oh lord he’s probably like 16! I would get my ass beat if I talked to my mom that way! Plus aren’t they in high school? I couldn’t pull any of that after Elementary school, and even then I would dare

I did talk to my mom like this ╮(￣▽￣)╭ bcs when we talk seriously and formally thats mean something really bad happened.

I've definitely told my mum to shut up, but never in a context of us being in a genuine fight--it was always when she was teasing or deliberately being annoying. She also tells me to shut up in the same context, so fair's fair
╮(￣▽￣)╭

Lots of factors like culture and family dynamics, not to mention language has evolved. Telling someone to shut up nowadays doesn't necessarily have to have an offensive meaning. I grew up in a very strict household, so respectful language was mandatory and parents were parents, not friends. My best friend though, has a more friendly relationship with her mum, so she speaks more candidly. She also often tells her mum to shut up when her mum tries to embarrass her, but it's said in jest and not as a serious admonition.

Same. I always wondered why is he being so fuckin' rude toward his mom?!
"Shut up old hag", "it's none of your business" and all dat, I can't even imagine saying such stuffs toward my mother no matter how old I get lol. His mother seems so sweet on the other hand, I really feel bad.

Haha, your friend's relationship with her mum reminds me of me and my mum! For me, it's probably because it's always just been me and her. However, she's definitely still my mum--she always scared me sh*tless when she was mad, and I never talked back when she was genuinely mad at me. She would have bitten my head off, lol!