Now that you've asked... A couple of decades ago we had two young Australian girls from a choir stay over night with us. As a thank you gift they gave a jar of Vegemite, which they claimed was wonderful. I thought it tasted like ground up vitamins. I almost puked when I tried it.
They could not stand our Peanut Butter at all. Almost puked when they tried it.
I just took a look around the web for some of the “worst” food items and Vegemite comes up often enough to be a contender, maybe in the top ten? The “secret” seems to be to partake of Vegemite in moderation. I gather the more moderation, the better. ;^)