문찐 /mun-jjin/
Out of the loop / Culturally clueless
Someone out of touch with trends and pop culture. Used humorously to describe being behind on what's popular. A contraction of '문화 찐따.'
Examples
이 노래 모르면 문찐이지
If you don't know this song, you're totally out of the loop
나 진짜 문찐인가봐, 이거 첨 들어봐
I must be out of the loop — this is my first time hearing this