1. What does it mean?
반민초 adds 반, against, to 민초, mint chocolate. It describes a person or stance that dislikes mint-chocolate flavor, often contrasted playfully with the pro-mint-chocolate 민초단.
Also written or said as banmincho
2. The nuance
The mock rivalry is not a serious social division. Use it as light preference talk, not a reason to insult people or interfere with their food choices.
3. Examples
“나는 반민초라 다른 맛을 고를게.”
I'm not a mint-chocolate fan, so I'll choose another flavor.
“민초파와 반민초가 같이 먹으려고 맛을 두 개 샀어.”
We bought two flavors so the mint-chocolate fans and non-fans could both enjoy dessert.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.