This is a avery simple April Fools Joke. It can be played on anyone but the more intensely focused a person is the better. I used it on my manager and several others and I got everyone. Some play acting is required.

You need:
2 BIC Pens (you know the 100 pack ones you can get at the drug store)
a victim or two or three or four

Step 1: Open the Pen

Take the cap off the pen and gently pull on the writing part of the pen it should come apart fairly easily.
At this point you have:
a pen filler
a pen cap
a hollow pen with one plug in an end of it

Step 2: The Second Pen...

All you need from the second pen is the plug in the end of the pen. I gently pried my finger nail under the edge and it came right out.

Step 3: Assembly

Now take the plug from the second pen and press it into the empty end of the hollow tube from the first pen.

You can keep the actual pens for use as refills in other pens or deconstruct these after the joke and use them normally.

Step 4: All Finished... Now Go Find Your Victim

Place the either of the pen caps back on the double plugged hollow tube and it looks like an ordinary pen.

Finding your victim:
The best victim is an extremely focused individual.

ALSO try to get into theior office and hide all other pens this makes things really easy

Find several things you need to have them sign or mark up or something but state that it is very confusing and the they need to look at it carefully.

Hand them the documents and the 'pen' at the same time.

Generally the person will focus on the content and not even think about the pen.

When they get done 'examining the confusing document or sometimes even while they are examining it they will glance at the pen notice it is capped and uncap it moving the cap to the other end in preparation for signing.

They then go to sign and the see the pen is still capped so they uncap it again and move the cap to the other side and wallaaaa it is still capped.

Depending on how intensely focused on the confusing document they are, they may actually uncap the same hollow tube several times before they even catch on.

Note several of these pens can be placed in offices and the fun can last all day long.

You can even get the same person multiple times in this way.

HAVE FUN