Actually we say them sometimes,but not very often.

"Nali",you have known one of its meaning.That's correct,we can say it in formal,such as when we first meet someone or with someone we are not familiar with,and we try to be modest and polite.But we don't say it often.

"zhukou" is really rude,I guess that's why we can't hear it often.As to your refered situation,I think "算了吧（suan le ba)" or "得了吧（de le ba）” is ok.

Good luck! :)

即使相同的单词在不同的语言环境，含义也是不同的。

Question No.1

When someone compliments you or says you are good at something , you can appreciate it by saying 'xie xie' (谢谢) . Moreover, if you want  to show your modest at the same time , I think personally 'nali nali'(哪里哪里) is not wrong , but when you say it , you may speak naturally .

Question No.2

I think cultures and languages from different countries are the same in many cases . 'zhukou'(住口) is just like 'shut up' , when you speak it to your very closed friend with a lovely smile , he or she will not feel offended . It is really up to your expression and the situation you are in.

Hopefully my answer works on you .

Taylor xiexie！