Word/Expression: Skeletons in one's closet
Quick Translation: Secrets from one's past that one would prefer not to tell people about
A. Why are you so nervous about dating her? She's perfect!
B. It's just that I have some skeletons in my closet that I don't want her to know about.
A: 너 걔하고 데이트 하는데 왜 그렇게 긴장해? 걔는 완벽하잖아!
B: 난 걔가 알면 안될 몇몇 내 비밀들 때문에.
Possible Interpretation: A closet is usually where one stores private possessions to either keep them safe or hidden. Skeletons are symbolic of a person's past mistakes or guilt he or she carries. Hence, to keep skeletons in one's closet means to keep these things from the past away from other people.