<P> "Mad as a hatter" is a colloquial English phrase used in conversation to suggest (lightheartedly) that a person is suffering from insanity . The etymology of the phrase is uncertain, with explanations both connected and unconnected to the trade of hat - making . The earliest known appearance of the phrase is in an 1829 issue of Blackwood's Edinburgh Magazine . </P> <P> The origin of the saying may derive from: </P>

Where did the saying mad hatter come from