Which ingredient is NOT commonly associated with a Slippery Nipple cocktail?

The Slippery Nipple cocktail is traditionally made with sambuca and Irish cream liqueur, typically Bailey's. The drink is known for its layered appearance, which comes from the combination of these two ingredients. Sambuca, with its anise flavor, creates a distinct taste profile that is a hallmark of this cocktail. Bailey's Irish Cream adds creaminess and sweetness, making for a smooth combination.

Rum, while a popular ingredient in many cocktails, is not part of the classic Slippery Nipple recipe. This cocktail's identity relies on the specific flavors from sambuca and Irish cream, and adding rum would alter its intended taste. Grenadine, while often used in various cocktails for its sweetness and vibrant color, is also not part of the traditional recipe. Thus, the lack of rum in the Slippery Nipple cocktail solidifies it as the ingredient not commonly associated with this particular drink.