I LOVE COLLARS! I'm sure you've already seen Vixx's Chained Up. Here are a couple of my favourite collared K-pop videos you may not have yet seen:
REVEAL by The Boyz in which Juyeon wears a collar and a live performance in which he wears a collar AND a leash :D
HIT by Seventeen in which, at 3 minutes and 17 seconds, S.Coups not only has a collar on but RIPS IT OFF HIMSELF... *goes to the corner to hyperventilate*