Macmillan says can and could show 'you are annoyed.' Then in the next two cases: what are the difference in their meaning, when we assume that both imply the narrator's annoyance?
What can you be thinking of?
What could you be thinking of?
Macmillan says can and could show 'you are annoyed.' Then in the next two cases: what are the difference in their meaning, when we assume that both imply the narrator's annoyance?
What can you be thinking of?
What could you be thinking of?
I don't see any semantic difference between these two sentences.
[EDIT:] It's possible that can is a little more direct and suggests a rebuke because the speaker thinks the other person is thinking something odd, and that could suggests puzzlement rather than a rebuke.
In another pair that uses can and could, however, there is a difference in register:
Can you please close the door?
Could you please close the door?
The second one is slightly more polite than the first, but they both mean the same thing.