Emily Post's Etiquette, Chapter 9 Conversation, Phrases and Pronunciation, Slang

SLANG

The fact that slang is apt and forceful makes its use irresistibly tempting.  Coarse or profane slang is beside the mark, but the "movies," "deadly" (meaning dull), "swell" (meaning first-rate), "divine" (meaning pleasant), "hunch," and "O.K." and even such phrases as "and how!" "so what?" and "you betcha" are words and phrases in common use which would perhaps make our American vernacular stilted to exclude.

It must be remembered that all slang is so greatly modified by the tone of voice in which it is said that the vocabulary as printed may give an inaccurate impression.  Slang, to be acceptable, must be fresh and applicable or it is as unappetizing as a left-over buckwheat cake.   Moreover, it is like underscoring with written words, and to be effective must be sparingly used.

All colloquial expressions are little foxes that spoil the grapes of perfect diction, but they are very little foxes: the false elegance of stupid pretentiousness, however it is an annihilating blight that destroys root and vine.