In the broad field of entertainment, a running gag is a joke, situation or line that repeats. Running gags may also be connected to an event that occurred previously. Although the running gag is especially associated with situation comedies, it is also found in other forms of entertainment such as books, comic strips and films.
The 1980 movie, Airplane!, has Leslie Neilson's character, Dr. Rumack, creating a running gag with the line, "Don't call me Shirley." For example, a character named Ted Striker says to Dr. Rumack, "Surely, you can't be serious." Dr. Rumack replies, "I am serious...and don't call me Shirley." The surely/Shirley gag continues throughout the film. Striker says to Rumack, "Surely, there must be something you can do" and Rumack responds with, "I'm doing everything I can...and stop calling me Shirley!"
In the comic strip, Calvin and Hobbes, periodic references to The Noodle Incident are made throughout the latter part of the series. Readers are left to try to figure out what the Incident actually is and what it means to the character of Calvin. For instance, the reader may wonder if the Incident is related to the comic strip in which Calvin uses noodles for a school project about the brain when it's revealed that The Noodle Incident occurred at school.
One comic strip has Calvin worrying that he might not receive gifts from Santa because of The Noodle Incident. In another Calvin and Hobbes comic strip, the reader is told a strainer was a part of the situation. The information in the clues, like The Noodle Incident running gag itself, is very vague. The reader must rely on limited clues to try and figure out the gag.
Three's Company, the 1977-1984 situation comedy, had many running gags throughout its seven year run. The main one is Mr. Roper thinking that Jack is gay even though the other main characters know he isn't. Another running gag that involves Mr. Roper is that he is the only character to speak directly to the camera, especially when cracking a joke.