common as an old shoe
(as) common as an old shoe
Lacking in manners or refinement. I can't believe he just put his elbows on the dinner table—why, he must be as common as an old shoe!
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
*common as an old shoeand *common as dirt
low class; uncouth. (*Also: as ~.) That ill-mannered girl is just as common as an old shoe. Despite Mamie's efforts to appear to be upper class, most folks considered her common as dirt.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.