A dandy (also known as a beau or gallant) is a man who dresses elegantly and fashionably, but that was not necessarily of aristocratic origin. He exaggerates his manners, including the way he stands and moves, and the way he speaks. He promotes himself. This is called dandyism. The word 'Dandy' was originally a version of 'Andrew'. The female equivalent is a dandizette.
The word dandy first came out in the Scottish verse of about 1780: