It's canon, for sure. One of the very first things KDJ says to YJH is that since he's older, YJH should address him respectfully....and I think "hyung" would be YJH's trump card in bed because it drives KDJ wild...KDJ would tease YJH relentlessly and not fuck YJH like he wants, but all YJH has to do is get past his own embarrassment to say "please, hyung," and all of the sudden he'll be folded into a mating press and pounded within an inch of his life...