when I was in college, my roomate worked for the computer department as and I.T. guy. Well, as an I.T. guy he had all sorts of adminitrative tools that the normal student didn't have.
One of these gems of a tool was the ability to view and type on anyone elses computer screen.

So one day, this guy comes into the lab to work on the computers. This individual is a born again Christian to the extreme. Carries a bible EVERYWHERE he goes, constantly reads it, and EVERYONE is going to hell unless they are like him. Very overboard. He believe in the sign of satan "666" and all that good stuff.
My roommate, Steve, logs in as an administator so we can see what he is typing on his computer (we are in the lab also btw). He is working on a religious paper of some sort. So we decide to have some fun with him...
As he was typing, Steve would interject big 666's in the middle of his document. Of course this confused the crap outta him, and he started to get a little worried look on his face. He deleted the 666's then looked at his notes.
While he was looking, Steve put in a couple of carriage returns and wrote....
"666 HELLO BILL, THIS IS SATAN.... SEE YOU REAL SOON...... 666"
I sh*t you not, his eyes got as big as 50 cent pieces, he put his hand over his mouth, let out a little squeek, and ran out of the room, leaving all of his stuff behind.
He never did come back to that particular lab..

We laughed for weeks on that one....