It involves getting a piece of obnoxious artwork and making three photocopies of it. The traditional one was a photocopy of someone's middle finger sticking up but certain unnamed people thought it would be appropriate (and perhaps more interesting) to go for something more heavy duty. The actual suggestions are hardly appropriate for printing here so we'll leave them up to you to think of. After getting three copies of the artwork in question one then attaches them end to end so that they look like three connected pieces of computer printout paper (use scotch tape). You then call the FAX number you desire and feed in the first sheet. This trick would work best after the place is closed for the day or otherwise unoccupied for long periods of time.
When the first sheet comes out attach it the same way to the last sheet. This will result in an endless loop of paper. What happens is that this keeps feeding into the FAX machine transmitting the same image. On the receiving end the FAX machine will most likely run out of paper, be prevented from receiving other calls, and be effectively neutralized.
Like we said before, don't do this as it would probably be construed as an annoyance phone call and/or misuse of telecommunications facilities.