in joke
  開玩笑地,鬧著玩地
  Joke, n.
  1. Something said for the sake of exciting a laugh; something witty or sportive (commonly indicating more of hilarity or humor than jest); a jest; a witticism; as, to crack good-natured jokes.
     And gentle dullness ever loves a joke.   --Pope.
  Or witty joke our airy senses moves
  To pleasant laughter.   --Gay.
  2. Something not said seriously, or not actually meant; something done in sport.
     Inclose whole downs in walls, 't is all a joke.   --Pope.
  In joke, in jest; sportively; not meant seriously.
  Practical joke. See under Practical.