Is Dal Dal cat ears is just hair accessory? Is there a reason that no one notice Dal Dal cat ears?
I'm not very familiar with the Korean traditions, but I don't think it's just a hair accessory because sometimes when she get excited she reveal a cat tail.
And I also remember there were some guy who cheer for Moon-Young who has a bear ears, so she couldn't be the only one (isn't?).
The answer comes from the wiki of this manga :




  Dal Dal always sports a pair of tiger ears. The tiger ears are
  actually detachable and are pinned to her hair. The author also
  sometimes adds a tail on her.