SUBREDDIT: r/tifu
TITLE: TIFU and earned the nickname 'The TCALL Kid'
POST: This happened a long time ago, but apparently that's ok, right?

In the late eighties I was working as a computer operator for a public utility company where they used a Honeywell Bull DPS-something mainframe which ran an operating system called GCOS. In the machine room there was a system terminal with special privileges which we used for kicking off backups and so on. We got word that a user terminal was 'stuck' and needed to be disconnected. Not something I'd had to do before but hey, how hard can it be? Apparently there's a command ('TCALL') for doing just that. So I type in TCALL and press enter, thinking it will show me the options for specifying which terminal etc. In fact, it disconnected every single terminal from the system, and it took two days to get them all connected again. Cost was estimated in the hundreds of thousands. And that's how I earned the nickname 'The TCALL Kid' and no respect from any of my coworkers.

From the [GCOS manual](

*TCALL - A GCOS system command entered at system console by operator to terminate interactive processing by users currently on system.
TL;DR: 
young, inexperienced computer operator caused one of those times when you're on the phone to your utility company and they say "oh, the computer's gone down, can you call back"