From just that little bit of information, I don't think there's anything terribly wrong. Is this new behavior? He's too old to suddenly have schizophrenia or bipolar.

He just sounds like an anxious guy. Maybe when he's cursing to himself he's just stressed about something. Talking to oneself isn't indicative of a disorder. I talk to myself every day. I always have. If someone caught me doing it, I'm sure I'd sneeze or do something else to pretend I wasn't just talking to myself!

The excessive smoking is also indicative of stress. Try to keep his environment as smooth-sailing as you can. At least, don't be a source of stress yourself.