“용” derives from a verb 용쓰다 which basically goes with humiliation or indignity. 용쓰다: to strain (for nothing), to make effort (for nothing) to endure (physical) pain to bite the bullet = eat the crow 죽겠지 from 죽겠다(basic form) 죽겠다 = ~to death 배고파 죽겠다. = (I’m) starving to death 보고 싶어 죽겠다. = (I) miss (you) to death or I miss you like crazy. 죽겠지 is often used either when you tease someone or when you take a wild guess and By adding 용용 in front of 죽겠지, it's apparently used when you tease someone.