It seems that the term "duh" comes from a war-time BBC radio show called "It's That Man Again": Diana Morrison's "D'oh"
"More an ejaculation than catchphrase, "D'oh!" was the explosive parting shot of the character Miss Hotchkiss as played by Diana Morrison in numerous episodes from 1945 (series 8/166 onwards)[19] through to the demise of the programme in January 1949.[20] Miss Hotchkiss was Tommy Handley's stentorian and authoritarian secretary; her surname was taken from a make of machine-gun.[21] Despite her authoritarian nature, she was susceptible to the amorous blandishments of Handley. However, these would inevitably lead to a put-down,[22] and an explosive "D'oh!" would signal Hotchkiss' exasperated exit.[23]
"D'oh!" was added to the Oxford English Dictionary in 2004, largely in response to its much later popularisation in the television programme The Simpsons, although ITMA is credited with the earliest recorded use of the term.[24]"