I learned that Dumb isn't bad, unless it means retarded...Which isn't bad, unless it means ignorant.
Examples:
Positive Connotations [Black People]:
"That shit slaps retarded."
"Man, we be goin' dumb."
Negative Connotations [White People]:
"Shut the fuck up, retard."
"Are you fucking dumb or something?"
All in all, blacks seem more positive.