as phony as a three-dollar bill

Image acquired from Wikimedia Commons and used with permission. Image attribution: public domain.

Explanation:

In U.S. currency, there aren't any three-dollar bills. If somebody made a three-dollar bill, it would be obviously phony (fake) to any American who saw one. And If someone had a three-dollar bill, and he was stupid enough to try to spend it, agents from the Treasury Department would rush in, surround him with guns, and take him to prison! That's how phony it is.

Note: A person can also be as phony as a three-dollar bill when he or she says nice things to people, but isn't being honest.

When something or someone is obviously fake, we say that it (or he/she) is as phony as a three-dollar bill.

Example:

Jane: Hi Donna! Guess what? My boyfriend and I are finally getting married! He proposed to me yesterday, and he gave me this beautiful diamond ring!

Donna: I really hate to tell you this Jane, but that thing in your ring isn't a real diamond.

Jane: What do you mean?

Donna: I work for a jewelry store, and I can tell you for sure that your "diamond" is actually made out of glass. It's as phony as a three-dollar bill!

Jane: I should have known something was wrong when I saw my boyfriend come out of that toy store just before he gave it to me!

Donna: Just a suggestion, but maybe you should marry someone who has more than five dollars to spend on a ring!

Would you like a translation of the conversation above into your native language? Then you should check out Babylon's translation software (aff) which can translate many languages into English.