The sin is either in making hasty judgments based on insufficient information or hypocritically condemning someone for something you yourself are guilty of. Santa Claus is not guilty of either. Indeed, since he is St. Nicholas obviously he is already in heaven and not going anywhere else.
DISCLAIMER: Catholic Answers has turned over the archive to Catholic-Questions.org and no longer owns, manages, or moderates the forums. For additional apologetics resources please visit www.catholic.com.