Like A Bad Penny?

This morning at work someone made a comment about how so-and-so was like a bad penny and my boss asked what a “bad penny” really meant. I was shocked to realize that this is a bit of trivia that I didn’t know. A quick net search informed me of lots of people, bills, proposals, etc that were bad pennies, but not what the original one was. As I seem to have a short attention span today (read, I’m feeling lazy) I put it to you folks:

What is a bad penny, and why would one keep turning up? Have you ever turned up a bad penny? If so, what did you do with it?

My WAG is that is has something to do with a bogus/bent coin which, say, won’t work in a machine (remember when they took pennies?) or won’t be accepted by a merchant, will keep appearing with inexplicable frequency.

F’rinstance, if you have a single penny mixed in with your tollbooth change of 400 quartes dimes and nickels, it will turn up virtually every time you reach in and fish out a few coins.

People don’t like damaged coins, so if they get a “bad” penny (or any other coin) in their change they pass it on as quickly as they can. So the bad currency is circulated more than the good, and so it keeps turning up.

In case you haven’t worked it out for yourself, I probably should’ve added that it’s just another way of phrasing Gresham’s law.