An abbreviation for "Old Testament; don't care". In discussions of the legitimacy of the Bible, "ot;dc" means that the passage is no longer legitimate; the New Testament is all that matters.
Frequently, it's used sarcastically by those who don't consider any of the Bible legitimate, and who are anticipating the replies of those who do believe the Bible.
"When two angels assume human disguises and visit Lot, an angry mob appears and demands that Lot allow the mob to rape them. Lot refuses, but lets them have his virgin daughters instead. God rewards Lot for this; how is any of this okay?"