best do

(had) best (do something)

It is a good idea or in one's best interest to do something. I'd best get to bed early tonight, since I have to be at the airport at 3:30 AM. You best call your mother before she hears about your pregnancy from someone else.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

(had) best do something

ought to do something, had better do something. Mary had best learn to mind her manners. You best listen to what I say.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
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