Do you think he is serious in those comments on FB or are they just jokes? Many people have an odd sense of humor that can sound a bit immature. If he doesn't bring unwanted attitude into the office, I personally would not mind at all. If he is serious, I would perhaps just conclude he is not the person I would want to be friends with.

I had a therapist who posts a lot of weird stuff on social media and it bothered me because he ended up being just like that in his practice with me. Part of it was presenting a professional values but practicing something entirely different, and not being able to tolerate any challenge or criticism. But if he had been a good T for me, I would not have cared about his online activity. I think most people have quirks and do weird things in personal life and some get a kick out of showing it off.