1. What does it mean?
악개 shortens 악성 개인팬, literally a malicious individual-member fan. It refers to someone who elevates their favorite by disparaging other members or encouraging conflict. The objection is to the harmful behavior, not simply having a favorite.
Also written or said as akgae
2. The nuance
This is an accusatory fandom label. Do not apply it to every 개인팬 or use disagreement alone as proof that someone deserves it.
3. Examples
“다른 멤버를 공격하는 악개 댓글은 신고했어.”
I reported the hostile solo-fan comments attacking the other members.
“개인팬이라는 이유만으로 악개라고 부르지는 마.”
Don't call someone a malicious solo fan just because they focus on one member.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.