At Durham University in 2000, "net send hello" at a Windows command prompt caused a message box to appear on every Windows computer on the uni network. I gave myself up to the bewildered IT department immediately.
Reminds me off my early days of discovering Unix commands. Except this was on my first job in a Bank running SCO Unix; a decidedly less forgiving environment than a University. I was the unofficial assistant sysadmin (long story) and running banner "hello"|wall in the middle of a busy day at the branch caused a fair bit of confusion. Thankfully we were a young bunch and sysadmin let me off with a somewhat stern warning.
