Yes, they are highly vindictive. They care so little about so little, that when something they care about, whether it be a pet, a human, or an ideology, is threatened they lash out in a manner that is generally excessive no matter the crime. Sociopaths are highly methodical and as such can come up with some very creative and seemingly innocent, if not innocuous, manners for revenge. It's in your best interest, if you know someone is a sociopath to not needle them, but instead let them follow their own path unimpeded.