Worst one I've had is a windows update somehow physically brick a notebook, no idea how it happened but even after replacing the harddrive it would still get stuck in a weird boot loop trying to start off a non existant drive. My best guess is the update somehow managed to damage/corrupt the BIOS.
Now they shove untested firmware updates onto windows update, launch them automatically, tell you that your computer is going to be updating for an indeterminate amount of time and that while that's evidently more urgent and important than whatever you were using it for they're generous enough to grant you three chances to postpone the update for 30 minutes, proceed with the update anyway when you tell them to postpone, warning you not to unplug the computer or else, and brick your machine even if you didn't unplug it (and no, warranty doesn't cover it, buy a new one, you filthy consumer).
We have several HP laptops at work, and they're an absolute nightmare.
One time i decided that a Windows update was taking too long and decided to turn off the computer. Fucked. Wouldn't boot anymore. Had to re-install windows.