Write a nice intelligent fork cherry bomb. It eats up some process tables and CPU time, but still allows some modicum of real work to get done. Make the system erratic and unresponsive, but only for brief periods (a few seconds to a minute). Be sure and choose executable names at random (from a list of typical background tasks).

[Not Perl] Install VNC on the victim machine, remote in, type the odd character at critical times (password input, command line parameters), and have a stealth mouse war.