Actualy, if it's Shane we're talking about, alcohol is far, far more likely then a refference to African Americans.
Shane McGowan is one of the foremost Irish musicians of 20th century (definitely with the worst teeth), he formed a band combining punk music (like the Clash) with Irish songs in the style of the Dubliners, or Clancy Brothers, but also open to many world influences. Sadly, Shane is a serious alcoholic, having been exposed to the stuff since childhood.