If any of us are ever blessed with the chance to meet Jungkook, let's remember not to call the maknae, the 1997 liner, 'oppa' unless he TRULY is older than you.
He genuinely hates it lol and let's not anger the golden maknae, okay?
Personally I think its a little odd of non-Koreans to actually use the word oppa unless it is with a friend (like I have a Korean friend who loves for me to call her unni, so I do but with other people I've just met or with some of my other Korean friends I'd never use honorifics...) but if you are Korean or you feel comfortable using it, just remember to use it appropriately :)
In this video you can hear fans yelling 'oppa' at Jungkook. To which he replies, I'm not your oppa? you keep calling me oppa!' and then *semi-jokingly* he says that next time he will require all ARMY to bring their ID cards to prove they are truly younger than him and can call him oppa ;)
At a fansign a fan asked him if he'd rather be called Oppa or a baby (aegi/ 애기) and he chose baby LOL.