In year 10, a friend of mine saw our school network admin type the admin password in (he used his index fingers and typed in each character one at a time like someone with very little typing experience - this was 1998)
Anyway, I used this info to log in as the admin and I promptly deleted all of the student accounts in the school. Students around me immediately started complaining they couldn’t log in or access their assignments.
It was a stupid and immature thing to do.
Guess it’s a good reminder and lesson that you should always be careful who is watching you over your shoulder.