I was contracting at a big three automaker and they had retained just such a firm, possibly even BCG, to "restructure" the IT department.
So they had a team of overpaid consultants come and perform an analysis. I won't even get into the pointlessness of all that. However, the leader of the pack, the alpha male of the consulting team, would physically walk his laptop over to a printer near the admin's desk to print because the information was too sensitive to print over the network.
In true hacker fashion a buddy and I had recently discovered that you could telnet into the printers and with a carefully crafted command actually set the text on the LCD readout on the printer itself. (The spot where is usually says "Load Paper") So we actually wrote a program that would allow us to send any text we wanted to any LCD of a printer.
So of course, this self important consultant became our first victim of the prank. He hooked up his laptop and we starting sending text like "Loading Virus" to the LCD. It actually became a little frustrating because he wasn't noticing the LCD.
Finally, he looked at the LCD and we starting sending text like "Downloading files from computer". This guy just went into an absolute panic and after the first few seconds of frantic inactivity he got his act together and closed the laptop. Of course, that didn't stop the printer from "Downloading files", so he finally ripped the cable from his laptop to sever the connection.
He was in a panic for what I'm sure were some of the longest seconds of his life, but by then we were doubled over laughing just a couple of desks away and he caught on.
I will give him credit for taking the joke well and he never tried to push it up the food chain or anything to involve any management.