I once showed somebody how to send an out-of-office...
I once showed somebody how to send an out-of-office reply, only to discover he had one set up on his personal email that he had sent the test message from (In the days when your email client didn't worry about niceties like "only reply once to senders"). I got the job ("well you know who to speak to, John") of phoning IT to explain why the mail server was filling up...