Here in the Philippines, there are people who we refer to as pranka ("frank"). They are people who tell the "truth" regardless of the effects of that knowledge to the recipient, and inconsiderate of how that truth is delivered. Truth is important to them, a concept of unspeakable significance, or so they say.
I daresay, truth is not the only thing that exists in the world (and in the world of human relations). True, I'm not socially adept; in fact, I consider popular person-to-person/people rituals and social conventions as my weakness, but I do know that what we say and do to other people affects them more than we can imagine, and sometimes there are more important things in life than telling straight the plain and simple truth.
Take time, be considerate, think things through, and do not be so arrogant as to deem yourself the only purveyor of truth.
Simply put: be honest, but be nice.