Well, there were windowlickers on the long bus that I rode to school.  I think, though, that palmettodawg's assertion is correct.  There's no reason to refer to people as \"retarded\" as an epithet for \"stupid.\"
Besides, the mentally retarded have a physical and mental disability which causes them to act and think the way they do.  Other folks...well, they just don't have that excuse.    
            
            
            Red and Black, Win or Lose