When I was at university, some time ago now, we each had an account on a *nix system for assignments. I had a part time job changing tape reels for overnight backups. I had a lot of spare time, so I'd log into the computer system via acoustic coupler, sometimes for the purposes of working on assignments, sometimes simply to chat. Needless to say, the connection speed was pretty slow. I don't remember the speed. Probably 1200 baud.
At some point, some of us students realised that our tty devices were globally writable, and so we could send stuff to each other's terminals without bothering with programs like write or msg.
So one day, a friend of mine thought it would be funny to type the following command (inventing a device name corresponding to my terminal for the purposes of illustration):
$ cat /etc/wisdom >/dev/tty123
This sent the wisdom file over my slow modem connection to my computer screen. The wisdom file was quite a large text file. So this took many minutes to complete, during which time I couldn't realistically do anything except wait for it to finish.
He did genuinely apologise afterwards, I'll give you that.