2) Good catastrophytes desperately fear conflict of any kind because it will undoubtedly bring about the end of a friendship or, possibly, yelling. So the first response to this situation should be: stalling. You've been busy at work. You've been sick. You've been sick at work. You've really been feeling down. Pull them all out. If your friend persists, and some strong souls will, proceed to 3).
3) Clearly you cannot tell the truth. That would be both foolhardy and brave. And totally unnecessary. If you told the truth, your friendship would obviously either be finished or irrevocably damaged. If you've been passive-aggressively attempting to extricate yourself from this friendship for years, by all means, be honest. But if there's still something to be gained for you from this relationship, there's only one thing you can do: lie.
4) Lie. I cannot say this enough. LIE. Don't compromise your principles entirely; just lie a little bit. Let's try it. I loved your chapter transitions. The font choice was very believable. I always thought you'd be capable of writing such a book. Or, simply gaze at them, clasp your hands together earnestly and make low, keening noises. That can be interpreted in any number of ways.
5) This is yet another truly delicious catastrophizing scenario because it gives rise to a larger question. Why are you friends with someone who writes nauseating prose? How's your prose?
6) What's so beautiful about this is that it will have a lasting impact on you. If you are really convincing when you lie ever so slightly to your friend, you will learn never to believe any compliments paid to you ever again.