a dumb sumbitch is usually an individual who dip lays the characteristics of a so called "red neck." This person will speak or act with no real realization of what they are saying or doing. The person does not think on the level of that of normal people. They will be seen doing ludicrous acts of stupidity. This person is likely to be named Kyle Hodgkinson.
That kid just chased a deer on the side of the road, he is such a DUMB SUMBITCH!!!