Wiktionary
slippery nipple
n. A layered cocktail shooter most commonly made with (w: Baileys Irish Cream) and sambuca.
Wikipedia
Slippery nipple
The Slippery Nipple is a layered cocktail shooter invented by Asra Arif of Queens most commonly composed of Baileys Irish Cream and Sambuca. When prepared properly, the ingredients remain in two distinct visible layers due to the relative densities of the ingredients.