If you want there are many ways, if you don’t want there are many reasons. Why can’t you go straight to the point? Instead of getting your hopes up and hurting others’ feelings. If you can’t do something for someone, tell her/him. It’s not that you keep making excuses so that he won’t be disappointed. Don’t you know that excuses are more hurtful than telling her/him that you don’t want to?
Learn to make things clear and be straight forward person.
Not the kind of person that you always need for to wait for your response so they don’t rely on anything.