1. What does it mean?
맵찔이 blends 맵다, spicy, with 찌질이, a belittling word for a loser or wimp. People often use it self-mockingly to say even modest heat is too much for them.
Also written or said as maepjjiri
2. The nuance
The ending can be insulting when aimed at others. Spice tolerance is not a measure of courage, and nobody needs to eat something uncomfortable to prove themselves.
3. Examples
“나는 맵찔이라 매운 소스는 따로 받을게.”
I'm bad with spicy food, so I'll have the hot sauce on the side.
“맵찔이 친구도 먹을 수 있게 순한 맛으로 골랐어.”
I chose the mild version so my spice-sensitive friend could enjoy it too.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.