Worst Operating System Ever Made

Definitely Windows ME, it's also known as "Windows Mistake Edition". I got one crash per day back when I used it. Also:

Windows 8 (after Developer Preview) is also extremely bad, but hopefully 8.1 will make up for it.

Vista. Hands down (granted, I've only used XP, Vista, and 7). It honestly looked like an alpha version of 7 that never should have seen the light of day. The design was ugly, it was prone to crashes, and overall just bad. The core idea was good, but horribly executed. Windows 7 fixed all that, and that's what I've used for a while now.

OS number 1!: Windows 8, because... It's just a dumb iOS copy. :/ (I personally stopped using every non-free operating system and switched to safer free ones*.)

OS number 2!: Ubuntu (GNU)/Linux, for various reason. 1. They spy on their users. 2. Their graphical interface is just horrible. 3. They forgot to give the GNU credit for the OS.

OS number 3!: iOS, it's just... Too... Silly. It's not made for human usage, I swear. >_>

* : Think of free as in free speech, not free beer. :P