(Noun) Either a(n): complete clutz, an excellent person, a clumsy person, a foolish person, an idiotic person. Usually used when someone does something out of the norm, or foolish.
The "a" may be enhanced for effect.
Also may be used as a greeting. Occassionally substituted with Jma or j-j-j-jaaaaaaaaason maaaaa.
Will: I just knocked over a row or glass thermometers
Smith: What a Jason Ma!!