How did this not occur to me sooner? Take one of my favorite beverages, mix it with my other favorite beverage, add in some extra flavor and bit of time, and, well, the results speak for themselves.
Of course, there are coffee-flavored liqueurs out there. Kahlua is the most famous; it's based on rum, and tastes nice and sweet. But I like whiskey better than rum, and I want the complexity of a coffee liqueur, but not the inherent sweetness. By making your own, you can control quality of coffee, the amount of sugar, and the whole experience and overall flavor profile is totally a step up. And, it takes, like, five minutes.