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A milestone noting the passage of time since leaving a job or relationship gone bad that renders the original event irrelevant.

Once the amount of time since termination equals the relationship's duration, the annireversary has been reached and it falls into the black hole of time.
EX: You dated someone for exactly two years, and you broke up on November 5, 2011. You may celebrate the annireversary on November 6, 2013.
by RBelb October 22, 2013