In all seriousness, though, there are canonical characters who are rodents and insects. We probably should not be considering any humans.
Unless the question is who's the canonically weakest human. In which case I'd throw Isabella Swan into the ring.
(Twilight Spoilers I guess).
She literally can't run across a flat surface without tripping, and the one time she tried to punch someone, she broke her hand and her target didn't notice he'd been punched (her target was a werewolf in human form, but still). The only times she's ever effective in a hostility situation is when she's being self destructive--like stabbing herself, or meeting up with the vampire who wants to murder her.
--
Cats land on their feet. Toast lands peanut butter side down. A cat with toast strapped to its back will hover above the ground in a state of quantum indecision