I just found a useful post on AskMen.Com about giving constructive criticism. A number of the points in this article are relevant to our posting on dealing with a difficult room mate. In particular, the article mentions being empathetic and removing emotions and character traits from the discussion. Both useful approaches to dealing with a difficult room mate.
Check out the article and let us know what you think.
How to Give Constructive Criticism [AskMen]