Also an excerpt:

A 1939 etiquette book, The Correct Thing, a Guide Book of Etiquette for Young Men, by William Oliver Stevens, advocated that the proper young man “avoid monotony. Change pitch and tempo for variety. A slow steady drawl on one pitch will put any audience to sleep.” Stevens pointed out an even worse offense: “Tagging ‘uh’ after your words – ‘and uh…but uh’ – which is maddening to have to endure.”