How to reject someone nicely?

how do you tell someone that you don't like them?
without hurting their feelings

I am sorry to say that it is almost impossible to do. There are ways to be respectful, but if this person cares for you, when you tell them it is not mutual it will hurt. However being honest will hurt a whole lot less than avoiding the person or the subject.

Be honest, and brief
No need to tell them every reason you are not interested, just that you are not. If you care about their friendship, tell them that. If you don't care, don't lie.

Do it soon, do it in private, and afterwards respect their wishes if they don't want to see you for a while.

Best of Luck

be honest.
and nice...

...go somewhere private, so u can be alone, adn nicely them that person that u like them but only as a friend...

nicely break the news to them, I really do like you, but i cant go on liking you as my bf/gf. you will definantly find someone who feels that way, but that person's just not me. are you okay with that?
and thats all, no need to be all emotional. just short, sweet, and strait to the point.