That Christmas party staple - the backside copy - actually costs money:

Photocopier supplier Canon is warning customers to take better care of their office equipment during the Christmas period, claiming that the festive season traditionally leads to a 25 percent hike in service calls due to incidents such as the classic backside copying prank.

Not to mention costing a fair bit of pride later:

Geoff Bush from the north of England said one case he'd attended, where a young lady had cracked the glass mid-scan, also jammed the scanner so that it wasn't until the machine was fixed and her colleagues all sober that copies of her backside starting pouring from the machine.

I guess the copy repair guy knows all :) But wait - Canon has the solution:

Partly in response to this trend--or perhaps because of the "supersizing" of the western physique--Canon has now increased the thickness of its glass by an extra millimeter.

Heh.