But I was on a VAX tuning course in Reading. The course was okay, but not really teaching me anything new on the first day.
So, my neighbour and I decided to have a bit of fun and were logging people on the course off at random - we had our own server dedicated to the course. Then we were battling each other, seeing who could log the other off quickest.
We then broke for coffee and when we came back, I ran up a short script. The script was "innoquous" enough, it would list all logged on users into an array and any that weren't me got logged off. I ran it once, it worked perfectly. I then changed it to be a self-submitting batch job. Nobody could log back on, it was funny... Until I accidentally logged myself off (I had multiple sessions on multiple VAXes open and logged off the "wrong" session.
Anyway, what I hadn't thought about was, during the logon process, your username doesn't appear in the userlist, just a process id with "<LOGIN>". Oops. The script was busy terminating all the people logging on, including myself.
The lecturer saw the funny side, we then went into the server room attached to the lab and tried to log onto the console... You go it! No dice. In the end, we had to power down the machine and reboot!