One time I broke my mom's work computer by renaming the Windows (95 or earlier) system folder to be my name. She had to lug a desktop back to work on the bus so they could fix it. Sorry mom.
Also I loved to load executable files into a hex editor and look for readable symbols among the stuff that was beyond my understanding.
There was a bug in my hex viewer, though, where you could scroll off the end of the file and it would hexdump the next block on disk or memory locations beyond the loaded file instead. So I got very confused/paranoid viewing what I thought was the file from one game and seeing messages from another game or some of my own personal information.
Too bad I mixed up A and C while formatting... back then, nobody knew how to install an OS; machine was declared 'bricked' and when on the attick... it was 6 years before another PC entered our household...