갑분싸

When the mood suddenly shifts from fun to awkward — like the air getting sucked out of the room. One wrong comment, an uncomfortable silence, or a badly timed joke and boom — 갑분싸.

갑 = suddenly (shortened from '갑'자기)

분 = mood/atmosphere (shortened from '분'위기)

싸 = cold/awkward (shortened from '싸'해지다)