I really used to admire a girl at college a lot.. We had UNIX labs where you didn't have a GUI but just a Putty to a RHEL5 server in which each of us had an account. Once I was asked to help figure out the girl with something, and after doing it I just inserted this line into her .bashrc "echo "You are awesome!"". Everytime she logged in(we had two one hour sessions a week), she used to get that message.

There was also another guy I disliked and I just inserted "exit" into his .bashrc. Even the sysadmin couldn't figure out why his terminal was quitting as soon as it was opened and they finally had to delete his user account and then re-create it.