The most disgusting thing I've ever had is surströmming
From Wiki:
Surströmming (pronounced [sʉ̌ːʂtrømːiŋ], "soured (Baltic) herring"), known colloquially as Scandinavian rotten fish, is a northern Swedish dish consisting of fermented Baltic herring. Surströmming is sold in cans, which often bulge during shipping and storage, due to the continued fermentation. When opened, the contents release a strong and sometimes overwhelming odour, which explains why the dish is often eaten outdoors. A Japanese study has shown that the smell of a newly opened can of surströmming is the most putrid smell of food in the world, beating similar fermented fish dishes such as the Korean Hongeohoe or Japanese Kusaya.[1]
It's an tradition to surströmming in northern Sweden and when I worked there for a period of time, I was invited to a surströmming feast. I force fed myself a couple of bites, just to be polite and all.
the first pic shows surströmming in the can and the second pic how it's usually served: on bread with onion and potato.