<p>The truth is that you will never insult someone by calling them “Dr.” and I have seen some profs loose their marbles and throw things when addressed as Mr. (seems to be especially common in the Deep South)</p>
<p>The "Professor _____ is not used too much down here and in fact i dont think I have ever heard anyone addressed as such. This could run into problems as well if you happen to take a Dean who is teaching a class and suddenly you adressed them as Prof… could be another situation where they loose their marbles and start throwing stuff at you.</p>
<p>There seems to be a very relaxed attitude at many institutions however and calling your prof by their first name seems acceptable at some places (I especially found this in Texas, Oklahoma, and New Mexico… it might just be a regional thing)</p>