A weak fursona is a bat...how incorrect.
Being able to strike fear in to most human beings on the planet, hang upside-down for hours in length and even be used as the mascot for some of the most famous or infamous individuals that we have seen in our days, weak? Well, those who call you weak obviously have overlooked some important information.
Don't listen to those pricks, their full of rubbish anyways. The only reason they call you weak because of this: They may not be weak physically, but their minds, that's what is weak. Not sure if their self-image actually matches to other people's prospective of them, so in order to find some sort of security for their insecurities, they make fun of you.
It's either that, or they just don't think that a bat is strong, which to me, is a not very well formulated opinion on their part. So don't even think twice about what others say about you, because they are not your friends; not the ones that don't know the smallest thing about you.