The top of the hair hasnt got a "true" explenation either. I just played around with different shapes for a while, and came up with this solution:
The head is now complete and the final touch is seperating the green jacket from the black shirt. First lets do some reconcidering. Personally I dont find the bare stomach so um.. manly, so lets make the shirt a bit longer. Highlight the edges on the middle of the stomach (1), chamfer them and scale the upper circle out a bit. Set the new shirt to Smooth Group 3 (2). Continue by Selecting the Polygons where the jacket's opening is (3) and chamfer it about 1.5 units (4).
Change the polygons you see in frame 1 to what you see in frame 2 by either rebuilding them manually or using the Visible/Invisible tools in Edge mode. Select the edges ans shown in frame 3 and chamfer them (4).
Fix up the mess on the bottom corner of the jacket by welding the three marked verts (1) and moving the 4th vertout and a bit to the left (2). Then select the whole Edge of the jacket (3) and extrude it out about 2,5 units (4).
Lastly, select the edge that seperated the shirt and the neck (1), chamfer it, move the two parts away from wach other (2), set the polygon's Smooth Group to the same as the shirt, and fix the messy mesh as I've done here (3). Also set up the jacket's newly extruded polygons to a fitting smooth group (4).
This is how i set up the final Smooth Groups, each number in its own color.
Now lets make a beauty render. Add a Skylight object to the scene, and find a nice 3/4 view in the Perspective viewport. Go to Rendering -> Advanced Lighting, set it to Light Tracer and hit Render. VoilÃ¡.