Miss Manners: How do I turn down a date without hurting his feelings?

Dear Miss Manners: What is the proper way to refuse a gentleman’s invitation for a date? The little white lie seems wrong, and does not discourage the gentleman from issuing more unwanted invitations.

Is there a way to salvage his ego, particularly when one is genuinely appreciative of courteous and courageous efforts? Friends suggest calling him “buddy” or blithely referring to one’s current infatuation across the room. What do you suggest?