Now they're in my head, so... My other favourite responses to, "Do you know what you should do?" are:
This one is very funny for how it stops them in their tracks.
One said, "You do??"
Yes, I totally know what I should do, because I am me, and am aware of my life, my responsibilities, my commitments, my needs, my dreams...
Yes...I should go home and have a nap.
haha. Then they seem to realize I've just completed what is, in fact, a shit ton of work, lol. This quiets their thought.
Yes, I should go home and have a nap. What should you do?
Then they have an opportunity to think about their life, responsibilities, commitments, needs, dreams instead of those they imagine mine to be.
All of these are cheeky, yes, but (and) make me happy! And also keep the relationship healthy instead of resentful, imbalanced, etc.