I personally consider it bad to drink alone. Usually this would be associated with depression or alchoholism. I personally have never consumed alcohol alone, and honestly I don't see a point to it. Alcohol makes people funner to be around my reducing your inhibitions and "inspiring" people to have more fun. I guess the assumption (and its true in my case), is that if you are alone you probably aren't having much fun, and drinking when you are alone is done simply to forget about your troubles and get away from the world. I know its obviously not always true, but its true often enouhg that people come to the belief that drinking alone is generally a bad thing.