I am not sure why it is, but as I drive around, I am encountering more and more drivers who do not understand the right-of-way laws.  I am approaching an intersection, I am turning right, and all of a sudden, a driver coming from the other direction turns left in front of me, causing me to have to slam on my brakes to avoid a collision.  

What is going on?

Maybe they have noticed that at some of those intersections, there is a yield sign up for people turning right.  They may believe that refers to them.  It would if they had a green left turn arrow and I, as an oncoming driver, had a red light.  But I do not; I have a green light.

So, the general rule applicable to left turns applies.  It is set out at OCGA 40-6-71:

The driver of a vehicle intending to turn to the left within an intersection or into an alley, private road, or driveway shall yield the right of way to any vehicle approaching from the opposite direction which is within the intersection or so close thereto as to constitute an immediate hazard.

As I said in the title, drivers turning left go last.  So, no, the left turning driver does not have a right to cross two lanes of traffic and cut me off as I am near the intersection.  They should only begin their turn if there is room for them to complete the turn without cutting anyone off.