Baileys. Just pour couple of tablespoons into a cup of coffee.
OR, you can go with the more traditional Irish Coffee - pour a jigger of Irish Whiskey (bourbon or scotch can work in a pinch) into the cup. Add a generous teaspoon of sugar, and stir to dissolve the sugar. Leave the spoon in the cup, and pour in the hot coffee (the spoon dissipates the heat to prevent your crystal Irish Coffee mug from cracking). Stir well. Then top with whipped cream, and do not stir it in.