I used to work in customer services at Boots head office and someone once posted a prawn sandwich. The smell of that jiffy bag being opened up remained with us for weeks.
You could very justifiably have reported them to the police for sending offensive materials in the mail - whether that was the intention or not.
A friend of mine works in a hospital lab where one of the (delightful) jobs is to analyse poo samples. Patients are given a small plastic tube with a little scoop in it, so that they can scoop off a tiny bit of their turd and then seal it inside the tube and put it back in the clear bag to send away via their GP. When the lab receive it, they transfer it to the analyser machine.
The number of people who just crap straight into the bag (and it often clearly wasn't a clean drop) and then close it, like it's a goldfish they've won from the funfair, and send their massive jobby in, expecting an actual human being to reach their hand in to the bag to retrieve it. Some even put the form in loose with the dump in the same bag, as everybody wants to process and file away a stinky piece of paperwork encrusted with a sirreverence....
Of course, samples like this have to be dropped unopened straight into the hazardous waste bin, with no way of letting the GP know it had to be rejected if the form was tucked into the bad stuff. The lab had a furious complaint letter from one man some time ago - the first they knew about him, as his forms had obviously never been readable to identify him - calling them unpleasant words and accusing them of not being able to do their jobs (quite ironic, really, that part....).
All because, instead of a single tiny little scoop, sealed inside an appropriate container, as clearly directed in the accompanying 'how to' info, he'd been repeatedly sending them disgusting great big bags of loose cronk for the past few weeks. Apparently, the patients post them into an opaque box at their GP surgery and the box gets delivered to the hospital labs unopened.