I can't think of anything truly bizarre or inherently gross I've eaten, but I once was incredibly displeased to find that the chocolate pudding I'd gotten as dessert at a restaurant had shaved coconut in it -- but that was more of a texture issue. I also find pickled beets repulsive and I will not eat them.
I'd be fascinated to see some of the people in this thread try the flavor strips that are used to test if a person is a super-taster (someone possessing a higher-than-normal density of taste buds per square centimeter on their tongue). The strips are just little strips of paper (they kind of look like litmus paper) soaked with a compound that tastes more and more bitter the more sensitive your sense of taste is.
A few years ago, my household ordered a test packet out of curiosity, and the five of us tried them. One person was a non-taster (fewer than average taste buds) and couldn't taste anything. The test strips just tasted like paper to him. I and another housemate concluded that the strips didn't taste good, but weren't the worst things ever. My husband and my best friend tried them... and raced for the sink to rinse their mouths out. They both include those test strips as among the most bitter things they've ever tasted. (And no, I don't think some strips were more bitter than others -- we only got two strips and had to cut them up to make sure everyone got some, so some of us were tasting parts of the same strip, and having very different reactions.)
Just in case anyone's curious: https://supertaster.com/