What does “sseokso” mean in Korean?

썩소 is the smile that isn’t one: one corner of the mouth lifted, nothing warm behind it. It shortens 썩은 미소, “rotten smile,” with 소 being the Sino-Korean 笑, “laugh.” The word spread in the early 2000s as the counterpart to 살인미소, the “killer smile,” so calling a face a 썩소 says the charm has curdled into a smirk.

In the clip the actor playing 가영 explains that her character barely knows how to smile, so what comes out is always a 썩소 — blank by default, and a crooked half-grin when she gets excited about smashing a lamp. A related put-down is 썩은 표정, the face of someone who has visibly given up.