Like many things, good coffee need not be adulterated with dairy, sugar, or anything else. Good coffee that's brewed properly is smooth, not bitter, flavorful, with nice body, etc. Unfortunately, most people drink instant or some preground nonsense that you scoop out of a 6 month old can. It's so stale all you have left is the caffeine, and that's largely what makes it bitter; there are no solubles left to balance it out! Even your least expensive Costa Rican, Mexican, or Brazilian coffees taste far, far better than what you get in a can. Keep in mind that the preground is usually of the lowest grade coffee with all sorts of foreign matter (leaves, twigs, etc. that are all ground up).
Solution: Find a local roaster or buy from someone reputable online.
I'm mostly an espresso drinker, but if I do drink regular coffee it's usually a fresh Ethiopian Yirgacheffe in a vacuum or press pot.