MAC OS installed instead of Windows
There once was a clever website created by a graphic designer in Germany. The minute you entered the website URL in a browser, it would take over the entire screen, and appear to be rebooting into DOS, uninstalling Windows, and installing MAC OS.
The end result was a full screen image of the MAC workspace/desktop including some seemingly functional menu tabs and icons, and the only way to get out of it was to press ESC.