@anamur-- I think that being angry due to the diagnosis often happens to children who develop type one diabetes and do not understand why they have to take injections all of the sudden.
The anger associated with type two diabetics who develop the condition when they're older might also have to do with accompanying chronic conditions.
For example, my mother, who is sixty, has both type two diabetes and high blood pressure. High blood pressure also causes anger, mood-changes and impatience. It's common in diabetics due to the damage that diabetes causes to the cardiovascular system.
In this case, the anger probably has more to do with high blood pressure than diabetes.