I'm personally more used to people hearing about chimpanzees and thinking of them as bloodthirsty and predatory, not to say that this is a majority but definitely not knowledge limited to zoo nerds. I think the older people who think of them as harmless are from the days when Bubbles and the Chimp Channel were still common, but those practices have ceased being publicized, and the Travis incident gained a LOT of attention. They have also been overshadowed by gorillas and orangutan.
The animals that come to mind as most underestimated are pinnipeds, otters and penguins. Piscivores tend to be seen as relatively harmless to humans, I think partly because eating fish doesn't feel to many people the same as eating mammals or birds. I've never seen anyone call a seal 'harmless' of course, but I don't see many people bring up how horrifying it would be to be dragged underwater by one!