혜영: 형님! 제가 아주 귀중한 정보를 들었어요.

Kyung-ae! I heard something really important today!

경애: 뭔 속을 뒤집으려고 또?

What upsetting news do you have for me this time!

혜영: 제가 형님 속을 자꾸 뒤집어서 형님이 생각이 유연해지는 거예요. 사람이 자극을 자꾸 받아야 머리도 좋아지고 치매도 안 걸리는 거예요.

You’re becoming more open minded because I drive you nuts! You have to keep getting fresh stimulation to keep your wheels turning and your brain sharp!  

경애: 말은 청산유수야.

You’re such a smooth talker. 

혜영: 얘기 안 할게요. 어차피 형님 들으시면 속상하실 거예요.

Okay, I won’t say anything. You’ll get upset when you hear it anyways.

경애: 어차피 말할 거잖아. 말해. 

You’re going to tell me anyways. Just say it. 

청산유수(靑山流水) [n] fluent speech (figurative) Eloquent speech, literally meaning the clear stream water that flows down a green mountain slope.

Semi-polite/polite – 말은 청산유수에요. 

>> This phrase is used to indicate that the other person speaks well and without interruption. Originally, "청산유수" means "green mountains and clear water," and borrowing from these natural images, it means to speak naturally, uninterruptedly, and smoothly.

>> The dialogue is showing a situation where a person who is really good at upsetting other people with her words, is offering really important information. The other person is refusing to listen, but she’s providing all sorts of reasons for why she should hear her out.