A fair question, answered here on the PrawfsBlawg. I tell mine on the first day to call me “sir,” but only if they ask. Scares the hell out of the freshmen. Mostly they address me as “Professor,” which I’m not since I don’t have a Ph.D. and I’m not on any kind of tenure track. It’s sort of a generic catch-all title. However, I do correct them if they call me “Doctor,” and I say, “I don’t have a Ph.D. I have to work for a living.”

(h/t: Instapundit)