I don't keep chickens simply because I prefer ducks. But I can't think of any entire breed that I don't like. Even knowing a bad natured individual doesn't mean the whole breed is bad.
I've got something to say about temperament, though. Temperament is inherited and where a bird comes from is going to have an effect on the temperament. That's because some breeders place a high value on temperament and some don't. The really large hatcheries probably don't even know what the temperament of their birds is. They aren't going out there and socializing with their flocks.
So, if you know a bird with a bad temperament, maybe it is just which breeder it came from and not the breed at all.
I bought a batch of cheap Swedish ducks from a large commercial hatchery for my freezer. If those were the only Swedish ducks I'd ever met I'd tell you to stay away from Swedish ducks. They are so high strung they verge on hysteria over absolutely nothing. They haven't had good feed conversion, I suspect because they worry their weight off. They run and flap and scream from even the slightest movement of anything. It doesn't have to be dangerous.
They are like a completely different breed from my fat calm friendly show quality Swedish ducks. If the only Swedish you'd ever met were my little exhibition guys, you'd be saying that Swedish ducks are the best ducks in the world. They are calm and curious and think people are just dandy, even people without treats. They have nice thick bodies and they are growing well and using their food well. They don't get upset over anything.
Case in point: one bad bird really has nothing to do with a breed as a whole.