I think like you said Ki it's subjective so it's hard to say whether someone has "bad" taste in music because to them, or to others, their taste in music might be perceives as "good."
However I would describe someone with "bad" taste in music not so much as someone who is narrow-minded in their tastes (who says it's "bad" if someone only likes one particular genre?) but someone who can't appreciate other types of music outside of their comfort zone. For example, my tastes in music might only be limited to a bunch of different genres. BUT, I can appreciate music outside of these genres even though I don't necessarily like it - I can appreciate it for what it is.
It's a hard topic to discuss though because it's totally subject to personal preference...
__________________
|