I'm not sure if this is the exact line but for me it's from the scene where gugudan's mina's parents chose to cover up their daughter's crime and then IU said.. "Your choice will burn your daughter's soul"... ha! oh so so satisfying....
Can't decide which was my top favorite but here's what I find as ultimately cute and funny:
In Episode 5, when GCS carried the ghost bride in his arms. JMW looked so pissed up and somewhat jealous, and while he's walking away, she uttered these words like she's complaining and being sarcastic:
"Goo Chan Sung, I see that you are strong enough to carry her but you used a wheelbarrow meant for cabbages to carry me."