I've always found hyenas disgusting.
It must be a racial memory thing. I know its irrational and sentimental, but other predators, lions, cheetah, leopards, even wolves and sharks, always struck me as noble beasts. But hyenas, in spite of their marvelous adaptations, always gave me the creeps.
Cockroaches have marvelous adaptations too, and even though I know they are basically harmless, they make my flesh crawl, more so than any other creature.