Noun
a joke that is appreciated only by members of some particular group of people
Source: WordNetin joke
Just as with the name "Cowznofski", Moxie itself (often in logotyped form) became a running in-joke in Mad issues of the period. Source: Internet
It's a neat little in-joke, let's just hope that lightsabers don't show up anytime soon. Source: Internet
As the town changed complexion and became more and more African American, the in-joke name that was whispered among certain folks was “the Inkwell.” Source: Internet
The second season episode, "Steel," includes a scene at Universal Studios where Face is seen looking bemused as a Cylon walks by him as an in-joke to his previous role in Battlestar Galactica. Source: Internet
In rare cases, a stand-in will appear on screen, sometimes as an in-joke. Source: Internet
Print. Another in-joke reportedly appearing in the Jefferies tube sets on the original Star Trek series are labels on the pipes marked "G. Source: Internet