"Just joshing you" came from the late 1800's and has a very interesting story behind it!

Josh Tatum was a deaf mute, but a very enterprising young man from the Midwest. In 1883 the US Mint came out with a new nickel. It was deemed the Liberty Head Nickel and on the reverse side had a large roman numeral V stamped on it. The new nickel did not have the word "cents" or "nickel" stamped on it. Josh Tatum noticed this and the fact that it was nearly the same size as the US $5.00 gold piece, which at the time was used as common currency.

With the help of a friend familiar in gold electroplating base metal, they turned these coins into a figurative gold mine. Tatum went from town to town going into shops, stores & mercantiles. He was very careful not to purchase anything that cost more than a nickel, where he would hand over one of these gold plated nickels. The clerk would accept the coin, and in most instances give Josh back $4.95 in change, which he happily would take. By the time law enforcement caught up to him, he had visited hundreds of towns & had amassed a small fortune.

The Law prosecuted him but ironically he was found not guilty on the most serious charges, because he only purchased items that totaled 5 cents, and because he was deaf & could not speak he never represented that it was a new $5.00 gold piece.

The same year, the US mint added the word "cents" to the Liberty Head Nickle in an effort to bring this type of fraud to a halt.

Hence the famous saying "you're not Joshing me are you"?