Nice hack in .ssh/authorized_keys to stop unwanted username from logging in
This is a nice hack you can do to so that you don't waste time typing ssh command only to realize you used the wrong username.
I find it useful when I omit the user@ portion in the ssh command, thinking that the id locally used is the same as the one I should be using in the remote system.
All you need to do is to prepend the line(s) in the ~wrong-username/.ssh/authorized_keys with the following string:
no-port-forwarding,no-agent-forwarding,no-X11-forwarding,command="echo 'Re-login as \"xyz\".';echo;sleep 5"
You just need to put that string right before each line, which would normally begin with ssh-rsa. Lastly, make sure to have a space between the added string above and the beginning of the line (i.e. ssh-rsa).