Accidental Innuendo: Lampshaded in the marathon episode. Shiro races out way ahead only to turn back because he's run out of white powder. Kou warns him that he shouldn't say that out loud in case a policeman hears him.
Earworm: The openings and endings of both seasons.
The live-action Village Chief and Hoshi who appear in episode previews. Take account they are prop masks that look as realistic versions of the characters' masks, but they don't move as their animated or drawn counterparts... making them even more creepier.
The drama and its movie sequel don't follow the live-action aesthethic used by Studio Shaft in the anime for Hoshi or the Village Chief, and the staff decided to go for make-up for the characters... but it's not a pleasant experience seeing the heavy yellow and green make-up on Takayuki Yamada and Shun Oguri's faces, respectively.