I talk to myself...a lot...I heard its common though, please validate my insecurity about being crazy?!
I talk to myself as well, although I don't know about you but I'm an only child so I literally have no one else to talk to. I also find it easier to organise my thoughts if I mutter to myself while I work, drives my friends insane.
Other than that, I don't really act any differently when I'm alone, about a year ago I decided I didn't care what people thought any more, I was gonna do and wear what I wanted to, regardless of the abuse I got for it. Now I still get the odd comment but no one really cares any more and I'm so much happier.