My brother works for a local tech company. Whenever a new hire comes on, someone is responsible for setting up their office and showing them around during the first few days. The people there have a pretty sweet set up with large thin dual monitors. But, we decided to have a little fun with the set up and replace the new hire's awesome monitors with an old-fashioned CRT.

We did this a while back, so unfortunately I don't have quite as much documentation as I'd like.

Materials:

CRT monitor
Computer that can accept DVI input or a DVI to VGA/HDMI adaptor.
Hiding place for actual monitors.

Step 1: Gathering Materials

I was able to dig an old CRT out of storage, but you could probably find one on Freecycle, a local tech swap/recycling place, university computer lab clean outs, or your grandmother's basement.
Newer monitors and computers have different ports than many older monitors. This particular monitor was DVI only, but the computer it was hooked up to did not have a DVI port.

If you have trouble finding either of those for free, there's always eBay and Craigslist. I had a number of CRT monitors and converters come up on eBay for around $10 for a monitor or $1 for a converter. (Search for "CRT monitor" and "DVI to VGA", sort by price+shipping: lowest first.)

Step 2: The Set Up

We wanted to make sure the actual monitors were still in the new hire's cube, but well hidden. The new hire's office had a larger desk, a small table/desk, and a rolling filing cabinet. This set up provided the perfect hiding system. It's a little bit difficult to see in the photos, but the smaller desk/table is pushed all the way against the wall. The filing cabinet is not attached. It is on wheels and easily rolls out. By pushing the side of the larger desk against the smaller desk, there was a nice cubby space to hide the actual monitors. We used the rolling filing cabinet to block access to the real monitors to make it a little bit more difficult to find, but still easy to access.

We set this up on the weekend, during off hours to make sure we weren't caught.

See illustration!

Step 3: The Story

On the new guy's first day my brother showed him his new office. You could choose to either ignore the fact that there's a CRT or say something along the lines of: "Yeah I don't know what's up with that monitor. But, don't worry, I already sent in a request to IT. I'm sure your new one will arrive soon."

Hopefully your friends are better with pranks than my brothers' because they were a little heavy handed and gave away the location by lunch time.