Someone who always drinks too much and whose life is falling apart because of it. ... Some people seem to be just fine even though they abuse alcohol. Experts call these people “functional” or “high-functioning" alcoholics."
Even though we never see Sarahsober, it doesn't get in the way of her life.
Joe: "Wow, James is drinking and it's only 7 AM."
Mike: "He's a high functioning alcoholic. He says he needs it to function."
Joe: "So he's a severe alcoholic who needs help then."
