1. What does it mean?
맴찢 uses the playful spelling 맴 for 마음 and shortens the image of a heart being torn. It appears in reactions to a sad story, a difficult goodbye, or someone's visibly disappointed face. 맘찢 is another spelling.
Also written or said as 맘찢, maemjjit
2. The nuance
It can describe genuine sympathy or exaggerated sadness over fiction. The cute shorthand may feel too casual when someone needs serious support, so choose a fuller response in that situation.
3. Examples
“주인공이 혼자 생일 케이크를 치우는 장면은 맴찢이었어.”
The scene where the main character cleared away their birthday cake alone was heartbreaking.
“비 때문에 취소된 소풍 준비물을 보니 맴찢.”
Seeing the things packed for the rain-cancelled picnic broke my heart.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.