The Windows Registry.

Lets make a giant file that every application dumps all its data into!
Lets make the operating system use it as well so a misbehaving application can wreck your whole system!
Lets key everything with a GUID so nobody has a damn clue what anything is!
And lets categorize it so that every application has to sprinkle its data into 10 different places!

Windows Registry, I want the last 3 hours of my life back.