Instead of sending people the usual stuff, why not add an order for Surströmming, the worst smelling thing in all existence.
https://en.wikipedia.org/wiki/Surstr%C3%B6mming
>when i smelled it the first time (and last time), i couldn't believe my nose! i mean it is >so disgusting that changes your perception of Smell as a concept. you would >understand that actually someone might be killed just by smell! it is really strange.. of >course i might be a bit exaggerating, but still, i can't believe something that horrible >being produced, packed and sold ,,, and bought!
http://www.swedishfoodshop.com/food/herring/fermented-herring
https://www.quora.com/What-does-Surstr%C3%B6mming-smell-like
The smell is known to linger for an awfully long time, even if only a few targets actually open it even just to see what it is, they will regret it for the rest of their lives.