While you are considering all these seemingly appropriate “pranks” suggested in the answers I have read below, just keep a few things in mind. The package will never make it back to the company. These kinds of things are filtered out at the first Post Office where t are received. The company won’t have to pay for the oversized package, since it is not what the embedded code on the envelope covers. And most importantly, a part of the postal code states that it is illegal to use a pre-paid envelope “for any other purpose than that which is intended by the originator” (paraphrased, but you get the idea) At some point, rather than just throw these away, or for one that is particularly egregious, t might track the package back and decide to charge you with a Federal Crime. If you think it is impossible to get caught, be reminded of the prisons full of people who thought the same thing…… In other words, don’t do it. You will not accomplish your objective, and the penalty may be more than you might have imagined.
If I had known this, I would never have gotten it into the package.