The dogs that I have seen who were "mean" that I had personal experience with were Pointers, Chows and German Shepherds. And one Hound Shepherd mix. I have never had any experience with Pits. My thoughts are that some of the bad things are inherited but some are more the owner's fault. I think that is true of most breeds. As I have said before we raised and bred Chihuahuas for 20 plus years and what I have just said holds true for that breed. We tried to pick our breeding stock always from mild mannered chihuahuas. Puppy buyers have a lot to do with how a dog turns out. We have had people show up out of the blue with their grown chihuahua that they had bought from another breeder. They wanted us to tell them what was wrong with their adult chihuahua who would bite even the owner and their own family. Most were spoiled rotten but some just inherited a lot of bad traits. Some of course were both. I must confess that we did sell one chi who grew up to bite the man of the house when he attempted to spank one of the children in the family. Now, I have to brag on the few pointers that we owned........never had one who bit anyone.