As I've outlined over the many years we've produced these Automator tips, this fine utility can be used in powerful ways to make your work easier. However, in the hands of the office prankster it can also be used as a useful tool on the first day of April.
The following workflows require that you have access to your target's Mac and user account. No one but a fool would leave their Mac open in such a way, but finding such fools is exactly what April Fools' Day is all about, right?
The devious desktop
Automator allows you to choose any image you like and use it as a desktop pattern. Feel free to click on the image below to expand it to its full size. Click on the image and then drag it to your desktop to save it. If that doesn't work, Control-click (or right-click) on the original image in this story and select Open Link In Window. Drag and click from there.
Plant that image in a not-entirely-obvious place on your victim's Mac. Launch Automator (in /Applications) and in the template chooser that appears, select Application and click Choose. In the Finder, drag this image file into the workflow area. This creates a Get Specified Finder Items action that points to the image.
Now select the Files & Folders library and from the Actions column next to it, drag the Set the Desktop Picture action into the workflow area. Save your workflow and in the sheet the appears choose Application from the File Format pop-up menu, give it an innocent-sounding name such as "Clock Sync," and save it to the same somewhat-hidden location you saved the image file.
Launch System Preferences, choose Users & Groups, click the Login Items tab, click the plus (+) button below, and navigate to the workflow you just created to add it. (No, you don't need to have the user's administrator's password to add a login item.) When the person who normally uses this Mac next restarts it, they'll find that their Mac sports a radically different look.
To undo what you've done: Remove your Clock Sync application from the account's login items. Control-click (right-click) on the desktop and choose Change Desktop Background from the contextual menu. Select the old desktop background.
The transforming Trash
You and I know that with Mac OS X, the Trash icon is now found in the Dock and not on the desktop. But if your friend is a Mac user from way back (or just not very observant), they may fall for this one.
Create another Application workflow. Select the Files & Folders library and drag the Rename Finder Items action into the workflow area. (When you see the warning, click Don't Add.) From the action's top pop-up menu choose Name Single Item. Configure the pop-up menu and text below to read PLEASE DON'T KILL ME!!! Save your workflow as an application and name it Trash.
As you did with the Windows desktop image, click on the image to see it full size, and then drag it to your desktop to copy it. (If that doesn't work, Control-click, or right-click, on the original image in this story and select Open Link In Window. Drag and click from there.) Open the image in Preview and press Command-A to select its contents and Command-C to copy them. Now select the Trash workflow you just saved to your desktop and press Command-I to bring up its Info window. Click on the icon in the top-left corner and press Command-V. The image of the trash will now become the workflow's icon. Place the file in the bottom right corner of the Mac's display.
When your victim drags a file to it--thinking it's the Trash--the application will do it job and cause the file to plead for its life by changing its name and refusing to go into this alleged trash.
(There's a practical use for a modified version of this workflow. Instead of using the Rename Finder Items action in the workflow, drag in Move Finder Items to Trash instead. Perform the same trick of assigning the trash image to its icon and place it where OS 9's Trash icon once resided. Now, when you want to work old-school, just drag unwanted files to this icon and they'll be moved to the Trash.)
To undo what you've done: Toss the workflow into the real Trash.
This last workflow requires a little subterfuge as well. Start by creating a new folder on the desktop and name it Macintosh HD. If no hard drive icon appears on your desktop, move to the Finder, choose Finder > Preferences and in the General tab enable the Hard disks option so that the Mac's hard drive icon appears on the desktop. Select that hard drive, press Command-I to produce its Info window, click on the icon in the top left, and then press Command-C to copy its icon to the clipboard. Select the folder you just created, press Command-I, select its icon, and press Command-V to paste the contents of the clipboard. Return to the Finder Preferences window and disable the Hard Disks option so that the Mac's real hard disk icon is hidden.
Create a new workflow and from the template sheet choose Folder Action. At the top of the workflow window drag your Macintosh HD folder to the Folder Action Requires Files and Folders Added To pop-up menu so that the folder you created becomes the target of the workflow.
From the Files & Folders library drag the following three actions (in order) to the workflow area: Get Specified Finder Items, Get Folder Contents, and Move Finder Items. Into the first action drag the Macintosh HD folder you created. In the Move Finder Items action choose Desktop from the To pop-up menu. Save your workflow.
What happens next? When items are dragged to this folder they'll be almost immediately spit back out to the desktop. Hilarity ensues.
To undo what you've done: Delete the folder. If the real hard drive used to appear on the desktop, open Finder's preferences, choose General, and enable the Hard Disks option.
This should go without saying, but I'll say it anyway: When pranking family members or co-workers in these ways, be sure that you're nearby and ready to undo your work. Additionally, to avoid an unwanted poke in the snoot, be very careful about who you select as your victim. Choose unwisely and the April fool may be you.