I can’t remember what I did to break it, but back when I was in high school I was tinkering right before class and rendered my laptop unbootable. I booted into an Arch Linux USB, chrooted into my install, found the config file I messed with, then reverted it. I booted back into my system and started the bell ringer assignment as quickly as I could. I had one minute left when the teacher walks by, looks at it, and says that I did a really good job. She never knew my laptop was unbootable just 2 minutes earlier.