Are you Chinese？666 means cool in China🇨🇳
I think 666 doesn't means cool at all, I'm Chinese sorry I just want to explains some misunderstand.
In my opinion, 666 in China in fact means like "shit" in English,
it can means cool also can means not kind to someone, maybe some attack in it.
I don't know I say is right or wrong, just want to let you know this word's means are too much, maybe you see this word next time you can learn more.
Glad to make you see all of these word, thanks.