Vicodin is a narcotic/opiate. As such, it is a respiratory depressant. That is not a big deal if you take it as prescribed, it usually isn't a big deal. If you mix it with alcohol, which is also a Central Nervous System depressant, you combine the two effects. This is a bad thing. What can happen is your body forgets to breath. So you pass out from "drinking too much", and never wake up -- or you get hypoxic injury to your brain (from not enough oxygen). The dose at which this can happen varies from person to person, and can vary from time to time in the same person. In other words: don't mix alcohol and narcotics. Even if you get away with it once, twice, or more, you never know when it will bite you...
Also, don't sell your prescription drugs. The person buying them could die from taking them due to the above scenario or for other reasons (vicodin is a mixture of drugs -- hydrocodone and acetamenaphen) like a drug reaction. Even if they take the dose on the bottle, the doctor writing the prescription wrote it for the person on the bottle: the dose could be different for the person who bought them illegally. In addition, selling prescription drugs is equally as illegal as selling illegal drugs.