On who sees beer as a lifestyle, culture, and/or art form.
One who takes beer seriously enjoys every aspect of it (The craft, creation, taste, aroma, design, brewers, breweries).
One who educates people about beer, real beer and opens them up to styles they never knew about.
Those who read beer blogs, beer review sites or follow breweries. Those who take more photos of beer than anything else. Those who review beers, or write beer based blogs.
Those who's social media revolves around beer.
Person A: "wow you know your beers!"
Person B: "Yeah, I'm a brewhead"