If you have an operating system you absolutely cannot stand, please post about it below.
Mine definitely has to be Windows 8, because of its excessive focus on touch-controls. Microsoft managed to fuck up the START MENU; how can you possibly screw up something so simple‽ They turned a nice, simple list of pinned programs into a separate unwieldy screen filled with boxes of mismatched sizes (some were squares, some were rectangles, with seemingly no reason given as to the size, strewn practically haphazardly around). It was immensely ugly and not at all convenient.
I'm still baffled why Microsoft decided to keep some of that repulsive bullshit when transitioning to Windows 10, with those intrusive "Live Tiles" on the restored Start Menu. WHY GATES WHY
Windows 7 > Windows 10 > Windows 8, and I've barely used 7!