Wikipedia tells me that radical honesty is:
Radical Honesty is a technique and self-improvement program developed by Dr. Brad Blanton. The program asserts that lying is the primary source of modern human stress, and that practitioners will become happier by being more honest, even about painful or taboo subjects. Blanton claims this form of honesty can help all human relationships since it "creates an intimacy not possible if you are hiding something for the sake of someone's feelings."
The Radical Honesty technique includes having practitioners state their feelings bluntly, directly and in ways typically considered impolite. For example, "I'm disgusted with you for X" where X is a statement of objective observation about the person towards whom the comment is being directed. People who practice Radical Honesty employ a collection of techniques to shift them out of acceptable norms of "white lying" for the purpose of having a more truthful relationship with themselves and others.
Meh, that doesn't sound too hard, right? I like the sound of getting to say what I'm thinking and having stuff work out well because of it, although I'm struggling to see how telling someone they are dull and painful to be around would help create intimacy in the relationship, but it might be worth a crack.
A little further reading revealed a ripper of an article from Esquire.com (I only read it for the articles), which you can read here I Think You're Fat. It's pretty long, but I thought it was an awesome read. While the article proved to that there is no way I've got the guts to try this thing properly, it highlighted to me that several of the people I like the most already seem to operate along the lines of radical honesty with pretty damn good results. Perhaps there is something to this whole thing, if you're brave enough to try it - fortune favours the radically honest.