Umm errr Uhhhhh? As Chad hinted simply one of the most over and mis-used titles in the Culinay Arts.
There are so many layers of education and experience to not only becoming and then progressing as a "Chef" it's hard to pinpoint.
Personally I'd like to believe that you earn the title not when you finish school but.... When you are hired to and have been able to succesfully apply the knowledge you have accumulated over a period of years in cooking techniques, food chemistry/science, recipe writing, menu design and costing, food/equipment/wares purchasing and control, managment fundamentals, kitchen design, sales and service, staff education and training, etc, etc, etc.
Then again, life and experiences have taught me that becoming a Chef is something you earn. The title doesn't make the person the peson makes the title. It should never self proclaimed and gloated over and it should never be used to make another feel insuperior or insecure. A Chef should always be willing to share knowledge and lend a hand in the advancement of others involving the craft. Being a Chef is realizing it as the last know "Nobel" profession and then acting responsibly within that manner. Unfortunately many out there are intent on reducing it to nothing more than the "Court Jester".
So the question of "At what point is one called a Chef?" Could be when, as a sign of respect, a peer addresses you as Chef instead of your actual name.
Okay standing up here makes me dizzy so I guess it's time to step down off the soap box.:)