I believe I work with a sociopath. He's a generally nice guy, very even tempered. He's one of my favorite people at the office because he minds his own business and sometimes has a funny comment or two. I think he is one due to his past and present occupations, and a few things he's mentioned about his personality.
As you say, we all probably meet lots in a lifetime, along with many other types of disordered people. I don't think there is a specific reaction from me. All people are the same until their disorderedness affects me.