Rejecting Offers is really Hard :(

One of the hardest things that I have had to do these past few days (and last year) is rejecting job offers. It is hard enough to get a job offer and you are just expected to pick and choose from them and then say "ahhhhhhh I don't want you" in a flash (to me that seems very cocky). I feel that because you say no to a company, they won't offer you another job in the future because they will think you didn't think very highly of them before. Not only that, but I feel that companies will treat you "just a little" bit different next time you want help from them.

***Yes I know most of you are going to say "Who cares about there feelings" for what I am about to say****
From some strange reason I always think that I am hurting their feelings and or making them upset for all they time and effort that they spent on me. I mean common who am I to them? They have much more important things they could've done if they knew I was going to say no and slap them in the face with a rejection.

****Yes I know that companies expect rejections from people they are trying to hire****
But if it was me in their shoes, I think that I would get a little bit mad for spending my time on someone who was not going to appreciate my offer. And this also brings up to another question: How do you go about in writing a "Rejecting an Offer" letter.