Just tell him straight in the eye that you two would be better off friends. But do it with a calm smile on your face while maintaining eye contact. It should work... worked for all the girls I've tried to date, haha...

"I think you are a great guy but I just don't feel that spark, and I don't want to lead you on."..
..
simple...honest...hopefully painless...

I have been in the same position before...
I found it hard to tell him because he was obviously very interested in me. I really liked him and did not want to hurt his feelings but I got the courage to tell him (over the phone) and he was understanding and actually appreciated it :)..
I think it would be wrong to give any other impression...
Hope that helps..
Helen..

the easy way is to be honest with him it may hurt but its better then beating around the bush or just avoiding him all together most people take it easier that way others usually are somewhat crushed but they will get over it. its better then a slap in the face..

This is a tough one. I am big on not rejecting people/hurt their feelings. I dont like to lie but I would lie if it were..so not to hurt this person. "Look the doctors are very positive that I might have AIDS; so I will call you once I know for sure."..