Try this in a new QuarkXPress 4.0 document on your Mac:
1. Draw a small rectangle textbox in the middle of a spread.
2. Use the Crosshair tool to select the box.
3. Hold down the Shift-Option-Command keys at the same time and hit Delete.
=) It also works in QXP 4.0 for Windows with Shift-CTRL-ALT, but it's not as funny in Windows...
[Update - 1721h]
Try doing it 5 times in a row. Thanks fanless =)