As genuine as a three-dollar bill
This idiom is used to describe something or someone that is not authentic or trustworthy. It implies that the thing or person being referred to is fake, counterfeit, or suspicious. The origin of this idiom can be traced back to the United States in the 19th century when three-dollar bills were not commonly used. In fact, there were very few instances where three-dollar bills were actually printed and circulated. This rarity made them unfamiliar and unusual to people, leading to the association of three-dollar bills with something dubious or questionable.
When someone says that something or someone is “as genuine as a three-dollar bill,” they are expressing skepticism or doubt about its authenticity. It suggests that the thing in question lacks credibility, sincerity, or honesty. It could refer to a person pretending to be something they’re not or an object that is a poor imitation.