"jukkesseo"(죽겠어) can be used in many different situations whether they are good or bad. Its original verb is "죽다."(die) But here, it doesn't have anything to do with "die". "죽겠어" means "overwhelmed by something" or "irritated by something intensely". When we use it in a positive sentence like "neomu yeppeo jukkesseo (너무 예뻐 죽겠어)", we mean the person we are talking about is so pretty and adorable. Boy friend : 넌 너무 예뻐 죽겠어. (You are so pretty. It kills me. =>It implies that you are the apple of my eye.) Girl friend : 정말? 고마워~ Another example in a negative sentence is like below. A : 우리 사장님 나에게 일을 너무 많이 줘. 짜증나서 죽겠어. (My boss (president) passes me too much work. It's so annoying. B : 그래도 열심히 해~ (You should work hard, though) I just come up with another example of it. 너무 많이 먹었더니 죽겠다. As I ate too much, I feel like dying. 난 네가 좋아 죽겠다. I like you so much. I can't express it enough. 엄마 나 힘들어 죽겠어. Mom, I feel so terrible that I feel like dying. Hope this can help you understand the magic word "죽겠다"

죽겠어 Is informal language and literally means going to die. if you say 너무 예뻐 죽겠어 it means (you are) so pretty (i am) going to die.