I'm irritated and annoyed. When I ask a question like, "would you be interested in something?", a simple yes or no would suffice. If I ask you to come somewhere, and you're busy or not interested, just say so. Politeness, my foot. You can be honest and still be polite, ya know?
And yeah, in case you don't know it, I know how to take a 'no' for an answer. At least, it's an honest answer. Much better than a non-committal, "let's see" or not replying at all.
If you have to waste someone's time, please waste yours. I have other uses for mine.