Authors:

The fact that slang is apt and forceful makes its use irresistibly tempting. Coarse or profane slang is beside the mark, but "flivver," "taxi," the "movies," "deadly" (meaning dull), "feeling fit," "feeling blue," "grafter," a "fake," "grouch," "hunch" and "right o!" are typical of words that it would make our spoken language stilted to exclude.

Emily Post (2007). “Etiquette: In Society, in Business, in Politics and at Home”, p.62, Cosimo, Inc.
The fact that slang is apt and forceful makes its use irresistibly tempting. Coarse or profane slang is beside the mark, but flivver, taxi, the movies, deadly (meaning dull), feeling fit, feeling blue, grafter, a fake,