At some point people figured out they could plaster another person's screen with porn via `xv`. But then someone else discovered that meant you could go in and Save File to the original user's directory. Once people realized that giving people write access to their directory wasn't a wise idea, this practice stopped.
xv was the wrong tool, there are others that would have been able to project images without giving the receiver the ability to write to your directory.
the most obnoxious would have been to set the background, because that's not easy to undo if you don't know how.
when i was a student i used to hang out in the computer halls until late at night. being one of the last ones there i was often able to get use of the one sun workstation that had a color screen.
one night the sysadmin logged remotely into the machine i was using and played "always look on the bright side of life"
