* Nulls in database strings

* Neckties

* Wikis

* Case-sensitivity in file names

* Case-insensitivity in programming languages

* Case-sensitivity in programming languages

* Differences in human preferences

* The marketers who create strange, confusing, and inconsistent version numbers/letters. "Do you want Foo X-Whammo Foo Super, Foo Semi-Whammo, or Foo Whammo X-Minus-One? We have a deal on Foo X-Enterprise Whammo and Foo X-Enterprise Whammo Extended. If you get it before Foo Doublewhammo comes out, you can get Foo Whammo Enterprise Express for the same price as the next version of Foo Whammo Zeron-Z with Gesture G5 and G-VI."