John Hughes, I can't quit you. In last summer's issue of Zoetrope All Story, Hughes recounted the creation of "Vacation '58," the short story that became National Lampoon's Vacation, which wrote on the sly while he was working at Leo Burnett:
The Lampoon's culture was similar to that of the ad agency--competitive but collegial; prodigal with clever, skillful writers and art directors. I liked my dual career and would have continued it had Chicago's Great Snow of '79 not trapped me happily in my house with my three-year-old son and preg-nant wife and hours and hours of time to write without having to keep an eye out for the boss.Vacation '58/ Foreword '08 [all-story.com via waxy]
For a vacation-themed issue, I proposed a piece set in the days when toddlers stood on the front seats of cars and parents' cigarette ashes blew into the faces of the children standing in the back (or hanging out the open rear windows of station wagons). I had no story but enough anecdotes to get the assignment.
In my bedroom office during the snowstorm, I wrote "Vacation '58." My outline was a Rand McNally Road Atlas I had dug out of the trunk of my car. I plotted the shortest route from Detroit to the most distant continental U.S. destination: Disneyland in Anaheim, California. I determined how many stops a family would have to make on such a trip, and where those stops might be.
I wrote the first sentence--"If Dad hadn't shot Walt Disney in the leg, it would have been our best vacation ever!"--and the rest was automatic.