I have heard you can send messages to other users in Terminal with the command "talk" or "write". If you can in fact do this, how?
The command is just talk. It's disabled in OSX by default. See the comment at the end.
It will then open a split screen and ping the other person to chat to you. They have to be logged into your computer at the same time though. Given that most Macs are single-user, this is unlikely, but possible. Have a friend connect in via SSH or screen-sharing and give it a go.
write allows you to write straight onto the other users console. By default though users have it disabled. You can turn it on with 'mesg y'.
Then type away to irritate the other user.
These are pretty old unix commands. Been around on linux/UNIX for years and years.
The man pages will help you too:
man write man talk man mesg
You can test this on one computer by creating a different ID and opening up Terminal with two windows. In the first window log back into your box with the other ID:
Then write to the main users Terminal:
You'll see the text appear in window 2 of the Terminal
To get talk to work on OSX you need to enable it first. As root run this:
launchctl load -w /System/Library/LaunchDaemons/ntalk.plist
or, as a super user:
sudo launchctl load -w /System/Library/LaunchDaemons/ntalk.plist