The word 'bamti' that ILLIT member Wonhee used on her YouTube channel means something is tacky or a bit clumsy/awkward.
For example, when you're not happy with your appearance or a selfie, you might say, "Why am I so bamti today?" Or when an outfit feels tacky or overdone, you could say, "This outfit combo is so bamti." It's an easy, casual way to joke about everyday moments.