This word was created by Jeon Jungkook, the youngest member(maknae) of BTS (a boyband from South Korea). The word "Apo! Bangpo!" translates to the short form in Korean for "ARMY forever, Bangtan forever".
(PS: ARMY is BTS's fandom name, and Bangtan sonyeondan is what BTS stands for).
For instance;
ARMY uses "Apo! Bangpo!" among themselves and to towards BTS to show affection. BTS too uses this to express their love towards fans.
Noun, a person who does not care whether their groceries are packed in paper or plastic bags. Adjective, describing one's lack of preference for either paper or plastic bags at the grocery store.
Paper or plastic you ask, well since I gave my reusable tote to a pet rescue, you pick, after all I'm bagnostic.