Okay. So.

Here's what I like to do:

First, locate two individuals somewhere at your company who have come to despise one another over the course of time.
For this demonstration, I've chosen two people from the finance department.
They're responsible for different things. They don't always work together, in fact they're just vaguely aware of each other's presence. They're just far enough apart for this trick to be successful.
Some morning, before either employee arrives at work, take a stroll by their cubes. Steal and swap their respective nameplates.
The targets will show up before either has a chance to grab his precious coffee. The first thing they'll see is somebody else's name. Someone who's name certainly doesn't belong there on the outside of their cubicle.
What the fuck?
What the hell's this?

I don't need to be looking at this. And where's my nameplate?

Is this some sort of retarded office joke?

I don't think I
find it funny!

  		IS THIS THE PERSON WHO'S BEEN ASSIGNED TO TAKE OVER MY POSITION??

Have I been fired and I just don't know it yet?

G-G-G-GOSH!! I HAVEN'T SAVED UP FOR SOMETHING LIKE THIS!!
Do I dare say something? Or will that just worsen matters, alerting the wrong people to my attention?

DID I GET CC'D SOMETHING IMPORTANT AND I WAS TOO SELF-ABSORBED TO READ IT ALL THE WAY THROUGH?

OH SHIT!!!
WHAT'S HAPPENING
TO MY LIFE???
Neither will attempt to interact with the other until it becomes absolutely necessary.

All day long, the hideous, awful word NAMEPLATE will clonk around in their heads, while each tries to solve this mystery.
When they finally meet, it will be only a brief confrontation, over in like five seconds.. but sometimes that's enough.

Each will genuinely believe the other is responsible. Each will have even further reason to dislike his colleague. 
They'll meet awkwardly and perform the exchange, without a great deal of predictable dialog. Their shared, unspoken opinions will be along the lines of, "Whatever, dude!!! Playing nametag games like a fucking retard!!! Real mature!!!!"

Remember: these two hate each other so perform this trick EVERY SINGLE DAY.