David Zucker sez:

In writing “The Naked Gun 2.5: The Smell of Fear”, I relied on 15 simple rules formulated in 20 years of writing, producing and directing comedy with my brother, Jerry, and partner Jim Abrahams. It has been said that comedy is all but impossible to teach – I have never once read a book about it – but we found it was possible to list certain things not to do. These rules are listed below in no particular order. And please don’t try them at home.

1. Joke On A Joke. We never try to do two jokes at the same time. When Leslie Neilson, who plays the role of Lieut. Frank Drebin of the Los Angeles Police Department, delivers a punchline, he always does it straight; he never tries to be funny on top of it. Likewise if there is something going on in the background, the foreground action must be straight and vice versa.

2. Unrelated Background. A joke happening in the background must be related in some way to the action in the foreground. A good illustration of this rule occurs in “Naked Gun 2.5” as Leslie Neilson complains to George Kennedy over drinks, “Is it just me, Ed, or is the whole world crazy?” As George tries to reassure him that “no, it’s just a small percentage of the population,” the waiter turns to leave and we see he’s naked under his apron. Unfortunately, half the audience fails to notice this because they’re still laughing at the silly drink the waiter has brought the lieutenant. This is a blatant violation of the joke-on-a -joke rule but at least now they’ll all have to come back to see the movie again.

3. Acknowledgement. Actors in the foreground must ignore jokes happening behind them. In “Airplane!”, Robert Stack and Lloyd Bridges engage in an argument, while behind them watermelons crash down from the ceiling and Indian spears thud into the walls. The actors do a fine job of ignoring the spears and watermelons, but because this bit violated Rule number 2 audiences still didn’t laugh. All in all a disappointment.

More at the link.