We had a kind of "computer club" back in a year. (AG in germany). The teacher left us (4 nerdy geeks) alone for a few minutes because he had to check on something.

He was still logged in with his IT-teacher account.

After a minute of reseach and a few little commands, we had our own school network admin account.

They still haven't removed (probably not even discovered) the account.

Sadly, the localgroup admin didn't have the highest rights..