The B-52 cocktail is a layered shot composed of a coffee liqueur (Kahlúa), an Irish cream (Baileys Irish Cream), and a Grand Marnier (in later versions replaced with triple sec or Cointreau). When prepared properly, the ingredients separate into three distinctly visible layers (due to their relative densities).

The B-52's widespread popularity has resulted in many variations, each earning a slightly different designation (see variations below for a small sampling). Altogether, the drinks are referred to as the B-50 series of layered cocktails.

The drink became a North London favourite in late 2009 when Arsenal striker Nicklas Bendtner changed his shirt number from 26 to 52, earning himself the nickname "B52" in the process.

More Info: en.wikipedia.org