10 informal phrases you can use to your Korean friends (which will make you sound like a real Korean) 

1. 그냥 그래 (걍 그래)

It means "so so" but many people type it 걍 그래 on Kakao [emoji] 

2. ~ 한 줄 알았어 

It's for exaggeration! For example, after solid workout session, you can say "다리 찢어지는 줄 알았어" or "죽는 줄 알았어" 

3. 아닌데? 

It literally means "no?" But it has meaning of "what you are saying/said is wrong". It has very specific intonation so listen carefully if someone says this! 

4. 말이 안 돼 

It means "It makes no sense", but literally means "it doesn't make words". You can use it like 말이 돼???? When you are showing doubt. 

5. 어이없다 

This one is tricky to translate.... It means "it's ridiculous" but with some disgust in it. You have to frown a little bit to make it sound more authentic 

6. 뭐 그런게 다 있냐 

It means "What on earth/what the hell ~ ?". We all have that time wanna say this right? If you wanna say it little stronger, you can say "뭐 그딴게 다 있냐?" 

7. 됐어 

It means "that's it" or "I'm done", or even "Whatever". Or you know, that "ugh, fine". 

8. 딱 기다려 

you wait right there! 딱! 기다려!

9. 콜

It literally means "call" but it means "I'm down" or "I'm in" 

10. 웃기지마