The third category is made up of your caricature stoner, who basically watches Cheech and Chong, Pineapple Express, Half Baked, and How High and tries to imitate what he sees because he thinks it will make him cool.
FYI, they do it because it's the only way to financially support their own personal [intense] habit, not because they think it makes them cool. Think about it, they smoke like madmen, then start buying more in bulk because it's cheaper, and then they start selling [for no profit] to their friends to be able to buy bigger, and then their friends' friends start asking and they start charging a profit etc...
Oh college, the things you learn in it