꿀을 먹은 벙어리

잔디: 아니 뭐 저런 미친놈이 다 있어? 그리고 이것 다들 꿀먹은거 아냐? 왜 다 가만있...
How come such crazy guys exist? And are all these people deaf and dumb? Why are they keeping silence?

This is ep 1 again, shortly after Gujunpyo spilled a bottle of juice on another boy's shirt.

다들 꿀먹은거 아냐 (haven't they all eaten honey?) is actually wrong, it's Jandi's version of 꿀을 먹은 벙어리 (a dumb person who's eaten honey), which means that a person knows about something but keeps silence about it, and this makes him or other people suffer.
The story behind this idiom is as follows: once there was a dumb man whose stomach was upset because he's eaten too much honey. His wife saw he was sick and asked him what happened, so he pointed to a jar of honey. The wife thought that he was asking for some honey to relieve his pain, so she gave him some honey with water. I think you can guess what happened next.
My bf told me a different story, though - he says that it's about a baby who's eaten too much honey and is suffering from stomach pain but cannot tell his mom about that because he's afraid to be punished. Either way it makes me wonder if overindulging in honey is really so dangerous for your stomach. No way I would try it myself though ^.^

A pun on Gujunpyo's name

This is a bit off-topic, but I couldn't skip it because of my obsession with names in Boys over flowers ^.^ Jandi shouts this in ep. 1 a few seconds before she discovers Jihoo is also there:

구정표! 이 구정물 같은 놈아!

Gujeongpyo! You are like dirty water!

She mispronounces his name (구정표 instead of 구준표), and so we get a pun - 구정물 같은 놈 is "the guy who is like dirty water". 구정물 is dirty water that is left after laundry (which is what Jandi's family is making their living from ^.^)

The real meaning of 준표 is bright + pillar, and 구 is a family name of one of the richest Korean families. The name is supposed to be well-suited for a leader of a multinational corporation :) It doesn't have the same meaning as the Japanese name (Doumyoji Tsukasa, 道明寺司 - way - bright - temple - to be in charge), but followes the same logic ^.^

입에 거품을 물다

This one is from 꽃보다 남자 ep. 1, where Jandi's mom tries to persuade her to go to Shinwa school and Jandi gets angry at her.

잔디: 엄마야말로 부자들 학교에다 돈지랄 한다고 입에 거품 물땐 언제구!
Meaning: Don't you remember how you were angry at rich people who are throwing money at this school?!

What it says: When was it that none other than you were foaming at your mouth saying that the rich are spending unreasonable money at this school?

입에 거품을 물다 means "to be very angry" and is very close to "foaming at the mouth" (it says "to have bubbles in one's mouth"). Another interesting thing here is 돈지랄 하다 - to spend money recklessly, which is from 돈 (money) + 지랄 (an epileptic fit, unreasonable behavior).

Some grammar notes: 야말로 is used to stress the subject (it was you, mom, who..., it was precisely you, mom etc.). 에다 has the same meaning as 에 (=at), ~다고 is used in reported speech, and 때 means "time, case" (땐 is short for 때는, 입에 거품 물땐 언제 - when was the case when you were foaming at your mouth?)

하늘을 찌르다

은재: 흥! 잘난 척이 하늘을 찌르더니...
Meaning: Huh! And he was so full of himself!
What it actually says: His opinion of himself was so high it could pierce the skies, but now...

은재 says this about 이준 when she thinks that he cannot find his way in Venice and needs her help.

There are two expressions here: 잘난 척 and 하늘을 찌르다.

잘난 척 is from 잘난 척하다 or 잘난 체하다, which means "to think highly of oneself", "to put on an air of importance". It's a combination of 잘나다 "great, distinguished" and  척하다  (체하다) "to pretend to".
하늘을 찌르다 (" to pierce the sky") means that something is sky-high. When referring to people it can also mean that somebody is elated or energetic about something, but here the first meaning (very high) is used.
Finally, 더니 is used when something changes or is no longer true.

죽으란 법은 없다

은재 learns that she will get a scholarship that even covers her living expenses if she passes the final exam:


은재: 죽으란 법은 없다, 현성야. 어떻게 이런 일이! 감사합니다.

I came across this one in Only You textbook (from Korean through Drama series). Unfortunately the textbook is for beginners only and does not explain it, so I had to search online.

The full form is 사람이 굶어 죽으란 법은 없다 (which basically means "a person cannot die from hunger"). It means that even if you are going through hardships or struggling to make ends meet, as long as you live you can always get some food to continue living. In a more general sense it means that there is hope in a most difficult situation. Another way to say this is 산 사람 입에 거미줄 치랴 (a spider cannot spin a web in a living person's mouth)