I work with someone who is clearly manic depressive and bi-polar. How do I get along with him?

He has worked here for about a year and a half. In the past 2 weeks he has been to the psychiatrist about 6 times and stayed in the psych ward of the hospital for two days. He is constantly changing moods. The day before he was admitted to the psych ward he thought he was on top of the world and had the best life ever. He has recently been doing a lot of research on anxiety and thinks that all of life's problems are a direct result of anxiety which EVERYONE is born with. He claims he is a chemically dependent person because he has to be on anxiety meds. Seriously I think some doctor should come do a study on him because he is so nuts. Oh, he also says very inappropriate things to everyone that works here about himself. He also has the answers to everything and compares himself to Einstein! When he first started here he was pretty normal and we were kind of friends. Now, I can't stand him and I have told him directly to his face that we can not be friends anymore because he is to eratic and moody to deal with. I work at a very small company with 7 employees and me, this guy and another girl work in a large room but at our seperate desks. I have to listen to him say random one word things out loud all day. And most recently he has started saying random words out loud in strange accents. The problem is he is constantly telling me and the other girl about the problems he is sure we have and how we should fix them. Neither one of us girls can stand to listen to him and he knows that yet he continues to talk! What do we do?