One day, after school, I decided to tinker with the Mac systems at my school, and in that process I learned that Mac has a virtual drive that it uses as a setup medium that it doesn’t clear, it just un-mounts, when you finish installing. So I just re-mounted the setup drive on the computer from the command line, restarted, booted in like I was setting up a fresh new computer and gave myself an admin account on one of the computers in our lab. Didn’t really do anything nefarious with it, but it was a fun little experiment regardless