Hey there. "I am crazy/cruel" is defining what you are. It is a saying you ARE cruel or crazy. "I am being crazy" is stating an action. You are doing something at present time that is crazy or cruel. But it does NOT imply that you are crazy or cruel.

I'm crazy/cruel = I'm crazy/cruel generally, not only now. being crazy/cruel = behaving crazily/cruelly now We use "am/is/are being " to say how a person is behaving ( something a person can control )

if you say im crazy/cruel - that is permanent it is the type of person you are. if you say im being crazy/cruel - that is one time. you just did it once and then you will be normal after