Out of curiosity, is it all olives? I have different feelings about green vs. black vs. kalamata, and even different feelings about the sub-varieties. I love some, tolerate others, enjoy some types in small quantities, and will absolutely avoid one of those little green ones stuffed with pimento unless it's floating in a strong cocktail.
They all do have a similar texture and oily quality though.
Very possibly escolar, a fish which shows up in sushi assortments from time to time, often mislabeled as a different fish.
Escolar flesh contains indigestible wax esters that cause oily diarrhea. Curiously, "escolar" is almost an anagram of "Olestra", the indigestible fat substitute that causes the same problem.
Escolar cannot be legally sold as food in some countries, including Japan. If it's in your sushi, don't go back to that sushi place.
I love sushi, udon, soba, miso ... but I can not for the life of me find a single enjoyable shred in the existence of Natto. Sorry but that stuff is just plain gross to me. It feels like eating a bowl of chunky snot.