Kopi Luwak is really expensive and among the most luxurious coffees that exist. And the reason why this sort of coffee is so special is it's method of preparing. Kopi luwak, or civet coffee, is coffee made from the beans of coffee berries which have been eaten by the Asian Palm Civet (Paradoxurus hermaphroditus) and other related civets, then passed through its digestive tract.
It is as bad as it sound, but nevertheless here's what one famous coffee critic Chris Rubin has said about this sort of coffee: "The aroma is rich and strong, and the coffee is incredibly full bodied, almost syrupy. Itâs thick with a hint of chocolate, and lingers on the tongue with a long, clean aftertaste".
The point is that coffee after this "process" doesn't have that bitter taste because when a civet eats the berries in its stomach, proteolytic enzymes seep into the beans, making shorter peptides and more free amino acids. Still, no matter how good it might taste I wouldn't dare to try it after seeing how it's made.