As anyone who's endured the company of the over-served can tell you, the rank breath that comes from having one too many is all about quantity. You probably won't notice the smell of one or two drinks, but as the number climbs, so does the concentration of alcohol in the blood ... and on the breath. Like garlic, alcohol makes its way from the blood to the lungs, and a breathalyzer -- and nearby noses -- pick up on it. Breath mints and mouthwash can't cover it up. The only thing that works is time.
Alcohol can lead to bad breath in a couple of other ways, too. First, alcohol consumption can lead to dehydration, which creates an ideal environment for the bacteria behind bad breath. Second, alcohol molecules can bond to the plaque that builds up along teeth and gums, making what's already a source of bad breath that much worse.