Advise on parenting problem and rude child?

Okay so I have this friend. She's a nice person, but the problem is, as her close friend, I find her a little not understanding to her children at times and now her child has grown to be like, 16 or 17, and he's really rude to his mom..not as bad as Eminem, but you get the picture.

My friend here always complains about her child, even in front of him.

I was staying over one time and she was teaching her kid mandarin. The kid mispronounced a word and she somehow thought that it was the cuss word "f*ck" and she proceeded to slapped him- twice. the kid looked like he wanted to cry. She uses swear words too, not that often though. And from my stay there, I know that she pushes her kid hard on studies.

Now that he's 16/17 I have talked to him for a few times and I have to admit he's a bright and analytical child, and very nice...that is except when he's angry. I saw today and it was scary. He was very rude to her and called her names. Weirdly, his argument made sense. His mother started telling people how lazy he was and he slammed his fork down on the plate and then shed him to mind his table manners so he said "don't tell me to mind my table manners when what you're doing is already embarrassing me." and mumbled "*****" What bothered me was the name calling. Though this is somewhat expected, I feel sorry for my friend. She's just very confused.

She is my close friend and I want to help her. And to be honest, she keeps calling me about all her troubles I feel tired of it cause I'm having a rough time on my own as well. Of all her problems this one struck me particularly interesting because I kind of understand that kid. I remember how I used to idolize my parents and they kept misunderstanding me (though they never hit me or cussed, and I didn't either) and I got so hurt and confused...but that's the past and I want to help my friend-and her kid. Don't worry, your advise will be used wisely, I'm not that type of person to push advise into people's noses. If they don't want it I always leave immediately. But all the same, I want to try, so what's your opinion?