Just where, exactly, does a circle start and end?

This question seems to be prevalent in many of the fundie answers I've seen when it comes to addressing god's origin. How do you counter? If one draws a circle, it has a start and end point; but if it's a doughnut, the center is simply punched out. Do the fundies have a good argument when they pull this question out of their bum? And, do you think they're being clever when they do so?