Linux Mint: removed all taskbars from the desktop. I was hoping it would just allow me to reset them to the default. But in reality, it breaks the GUI and it’s very hard to reset from the GUI. Suddenly my keystrokes weren’t being detected and I couldn’t open up applications with any sort of regularity. After a lot of dicking around, I got the terminal working so I could reset Cinnamon.
It’s not the worst way I’ve broken a machine. But it was one of the most annoying.