1. What does it mean?
A shortened blend of 멘탈 ('mental') and 붕괴 ('collapse'). In casual speech, it describes the frazzled reaction to a surprise, a mistake, or too many demands arriving at once.
Also written or said as 멘탈 붕괴
2. The nuance
The literal wording sounds stronger than many everyday uses. 'I'm losing it' or 'I'm overwhelmed' may fit better than a literal 'mental breakdown.' This slang is not a clinical diagnosis.
3. Examples
“저장 안 한 파일이 사라져서 잠깐 멘붕 왔어.”
The file I hadn't saved disappeared, and I panicked for a moment.
“주문이 한꺼번에 들어와서 멘붕이었지만 하나씩 처리했어.”
I was overwhelmed when all the orders arrived at once, but I dealt with them one by one.
Sources
National Institute of Korean Language
References support the meaning and usage. Example sentences are written for NoCapWiki.