This is something that I see debated often and probably will continue to be a topic of discussion; I think because there isn’t any one right answer. Odd characters are fun to write so writers like to create them. And odd character often speak in odd ways. Or if you’re trying to portray a certain group or character by their/the character’s speech pattern, trying to make them stand out, dialogue is one way to do that.
But as K.M. Weiland notes in the post below, if you use slang, or even odd speech ticks, I agree, that a little goes a long way. Part of the reason for this is you don’t want the reader to stop and have to really look at a word(s) to try and interpret what you’re trying to say. Text should flow easily through the readers mind. An odd word here and there probably isn’t an issue, but if you make the reader stop too often, they may decide they need to unload the dishwasher instead of continuing to read your book!
Authors need to get the nuances of slang in dialogue right, because smart readers will always recognize phony speech patterns.
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