You know what phrases like "a diamond in the rough" mean. Ever wonder where it came from? This site: http://www.phrases.org.uk/meanings/index.html explains it. According to the site, a diamond in the rough is clearly a metaphor for the original unpolished state of diamond gemstones, especially those that have the potential to become high quality jewels. It is more commonly expressed in the form 'rough diamond'. The first recorded use in print is in John Fletcher's A Wife for a Month, 1624: "She is very honest, and will be as hard to cut as a rough diamond." Here are my favorites. (Share yours. And some of them are pretty long. You don't have to post the whole thing. Just enough so it gives an explanation.) Mad as a hatter: Mercury used to be used in the making of hats. This was known to have affected the nervous systems of hatters, causing them to tremble and appear insane. A neurotoxicologist correspondent informs me that "Mercury exposure can cause aggressiveness, mood swings, and anti-social behavior.", so that derivation is certainly plausible - although there's only that circumstantial evidence to support it.