The reason I am flipping over Hobi's outfit:
The waistband hobi's wearing is called "Sejo-dae," an accessory worn by men during Joseon dynasty: the color shows the wearer's rank, and red is worn by first to third rank officials

Other members (I see Yoongi and JK here) are wearing "Norigae" here, a typical traditional Korean accessory usually worn by women. But men also wore them! There are millions of different design and they all have different meanings

These are all Noriagae, and actually it traces wayyy back in history pass Joseon dynasty. For men's Norigae they used to engrave wishes for longevity, fertility and prosperity

I have one that matches my bag