Whiskey dick is a slang term for alcohol-induced erectile dysfunction. Because alcohol is a central nervous system depressant, it slows down the nervous system, impacting most organs. Alcohol consumption also reduces blood flow to the genitals. This type of erectile dysfunction is temporary, and will typically resolves once the affected person sobers up. That said, "chronic and persistent" alcohol use can lead to long-term sexual dysfunction.
Although whiskey dick is the most common term for this phenomenon, any alcoholic beverage can cause alcohol-induced erectile dysfunction.