A shooter. Use a shot glass with a conical inside since the goal here is to simulate the appearance of a nipple. In addition to making a tasty shot, I mean.

Start with a dash of Grenadine. Float Baileys Irish Cream or Kahlua (depending on your preference) on top, filling about half of the glass. On top of that float Sambuca. Alternatively you could leave out the Sambuca and just use Baileys on top of Kahlua. If you make the drink properly your glass will have a red tip and a light brown, two-toned body. Shoot it.

The only place I have encountered this version is at Kappa Psi Upsilon. All the other variants (webtender and the like) leave out the Grenadine which I see as a crucial component.