Is honesty TRULY the best policy?

I am not a naturally nice person. Those that know me well can tell you that it is a constant battle for me to keep myself from saying something that I proably won't, but should regret later. One thing that does come easily to me is telling the truth. Something I've learned is that sometimes nice and truth don't mix. I tried mixing them and this was the end result:

Coworker: I never feel a very warm welcome when I come downstairs to the lit (litigation) department.
Me: Oh that's too bad.
What I'm really thinking: Probably because you're an awful human being.

Coworker: No I'm serious. I don't feel like anybody really cares for me on this floor.
Me: Oh I'm sure that's not true.
What I'm really thinking: If you weren't such a bad person people might like you more.

Coworker: No really, I'm not kidding. Tell me Kacey, do you consider me a friend?
Me: (using what I consider to be superhuman levels of restraint at this point)Sure.
What I'm really thinking: NOOOO!

Coworker: I'm not joking around. If you were at home telling a story to your husband that involved me would you call me your friend?
Me: Probably not.
What I'm really thinking: No. Not only would I not call you my friend, I would probably use lots of descriptive and possibly inappropriate words to explain how awful I feel you truly are.

Coworker: See now that offends me. It hurts my feelings that you wouldn't consider me a friend and it bothers me even more because I don't think you're alone in the way you feel.
Me: Oh my opinion doesn't matter, and I'm sure I'm alone.
What I'm really thinking: I'm not alone. I checked.

Coworker: No, I don't think you are. I've noticed that I am just not well received by this department.
Me: I guess you probably don't want to come around much then.
What I'm really thinking: Please don't come back into my office ever again.

I really did try to be polite, but something inside of me HAS to tell the truth. Please take note that I while I'm willing to attempt kindness, honestly always wins out with me. If you remember this simple fact, you might help both of us avoid an awkward conversation.