The putrid stench of death.

What is coffee-breath? Why are so many people able to imbibe huge amounts of coffee without ever suffering — or, more precisely, causing everyone downwind of them to suffer — from the condition, while a select few need only gulp a couple of mouthfuls of the stuff in order to smell like they've got a plague pit stuck between their teeth? Why do those people who do get coffee-breath not gag and suffocate on their own emissions, squirming to death? If they're aware of what's coming out of their mouths, why do they continue to drink coffee? And why do they always have something terribly important to explain to me in great detail?