Some one who is an alcoholic to such a degree that the alcohol has replaced their brain cells. Now, all they can ever remember or think about is aspects of their life and past related to their sad, depressed, alcoholic lives.
After he broke up with Girlfriend C, Jackass A became an alcotard. Now he doesn't remember anyone before Girlfriend B, not even Girlfriend A. He's such an emo dick. He's fucking Jackass B's girlfriend and getting high with his squadlings. None of his friends know him anymore and he doesn't know them. Because he's an alcotard.
A person who has consistently consumed large amounts of alcohol since teen-hood up until present thus hindering his or her own level of maturity from growing or advancing.