I have heard these called swimming pool coins. I have a dime that has this same damage. Apparently the chlorine in the pool causes this kind of damage to coins.
Do you think if someone called it a "junk coin" that they would be able to sell it on SleazeBay? ~ Chris
An extended soak in vinegar will do it. The acetic acid combines with the copper to form copper acetate which is water soluble and vinegar is 95% water so the copper core slowly gets eaten away. It can't attack the copper in the cladding layers as readily so the core core dissolves faster.
Welcome to CT @ROADDEVIL1. As already stated, PMD, post mint damage. It was damaged after it left the mint, so no error, and it is a good example of what a mild acid, such as chlorine, as @Lawtoad mentioned, can do to a coin. I'd keep it as an example.