Personally, I am a font of trivia. The guy who wins a lot at Trivial Pursuit. The guy who drops unbelievable factoids into conversation. And I’m just the sort of guy who sees that trivia as an important part of software testing.
Trivia, little known bits of knowledge, represents a particularly squirrelly test condition for a lot of applications.
Take, for example, this Forbes application, a map of the United States by county.
Ignore the obvious error that crops up:

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Well, if you’re testing the Web site, log it, but it’s not germane to our discussion (although it does further illustrate how Web sites run with errors obvious to testers even though one suspects someone looked at the Web site before launch).
Now, if you’re a resident of the St. Louis, Missouri, area, you might know that the city of St. Louis back in the late 19th century decided that it didn’t want to waste its tax dollars on the farmland around it and officially removed itself from the county. As a result, St. Louis County does not include St. Louis City, and in the beginning of the 21st century, the city wants access to the tax revenue of the metropolitan area and every couple of years tells the county that it would like to reconcile.
Here’s the county represented:

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That looks like it runs completely to the Mississippi River. Have they forgotten the city?
Kudos to them: they have not. Mouse around enough and you’ll find:

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Kudos to the developers of this application for knowing about the split. I would made the designer capitalize City to be consistent with other labels in the app, though. Note that the lines on the map are not supposed to be from the city of St. Louis but from a previous click on some county in Ohio.
Sure, you might say that this city/county split is basic knowledge that should be tested, and it is basic knowledge to most people in the government of St. Louis. But to someone in Massachusetts, it’s trivia. So the more regional basic knowledge you know from outside your region, the better.
What sort of trivia is best for testing? Probably not old baseball players and their averages. But geographical trivia and date-based trivia could be handy. If your software is international in audience, any insight into those facts of that foreign nation–trivia to most, but daily life to your users– could give you avenues of testing.
This last calls into mind what Mark A. said about a recent post about a children’s book and Mother’s Day:
The calendar is fine as long as the book takes place in either Paraguay (May 15) or Costa Rica (August 15), at least according to Wikipedia.
If you don’t have a stock of trivia accumulated already, Wikipedia is a good place to peruse. So is City-Data.com.
What your developers know can hurt them, and you can be the one swinging that hurtin’ outlier trivia.