The movie or TV show is over and all is said and done. Or is it? It might pay off to read the end credits, and you might discover a joke or two. A certain show even downright trolls its audience by breaking the fourth wall and adding remarks to the fans to the title card at the very end.
Grimm the inspiration for this trope does this a lot.
First season ended with a "to be continued" to which was added "sorry" Second season ended with "to be continued" and "Oh come on. You knew this was coming."
The season premier of the third season ended with "This ain't over yet."
Harry Potter and the Goblet of Fire has this hidden in the end credits: "No dragons were hurt making this movie."