It is quite easy to find a worst delicacy because there are so many dishes that people consider it a delicacy but they contain disgusting ingredients which is why they are the worst. Some of the ingredients are rare and hard to find or they are expensive. However, they either taste awful or sound like they would be awful, but they are included in a dish.
One of the worst delicacies is the Balut. It looks disgusting because it comes in a whole egg with the bird still inside. It is a duck egg and that grown inside the egg like most birds do except people usually tear the birds apart before serving it. In this case, it is served whole and is eaten with salt and lemon.
Kiviak is the name for a dish in Greenland and is not for the faint of heart. Basically, Inuit fishermen will capture and kill a seal. This seal is then disemboweled and covered in grease. After the seal has been properly taken care of, a large number of auks (a bird that is similar to a penguin) are also caught only to be killed and stuffed into the seal.
The seal is then sewn shut and covered in grease to prevent flies and maggots. Finally, the seal is placed into a hole, buried with rocks, and then uncovered after a number of months. If you're wondering what part of this is eaten, it's the birds. Every bit of them, including the bones and intestinal fluids.