(as) phony as a three-dollar bill
Completely and obviously false, fake, or illegitimate; not genuine or authentic in the slightest. (There has never been a three-dollar bill in circulation by the United States' government.) Primarily heard in US. The course claims to teach you how to get rich in a hurry, but I can tell it's as phony as a three-dollar bill. The senator's hammed-up, teary-eyed speech was phony as a three-dollar bill, if you ask me. The guy said he was selling Rolexes, but this thing is as phony as a three-dollar bill.
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