In a recent podcast of .Net rocks (at 45 minutes 29 seconds), regarding the future of software craftsmanship, it is postulated that there will be an 'Iron Ring Event' (if I heard it correctly). From the context it seems that this is an event where very bad things happen due to poor workmanship. Is this is a common term? What is its origin? What does it mean?
It probably refers to the collapse of the Quebec Bridge:
In 1922, Canadian Herbert Haultain created a ceremony for new engineers. New engineers are asked to recite an Obligation to their profession. They also are given an iron ring to wear on their little finger. The ring is a symbol to new engineers. It reminds engineers of their pride in their profession and their responsibility to safety.
The idea that engineers needed to be more responsible may have come from the Quebec Bridge disaster. The Quebec Bridge collapsed in 1907, killing 75 workers. The cause was an engineering error. In 1917, the rebuilt bridge collapsed. This time, 11 people were killed.
Outside of the North American (Canadian, in particular) engineering community, I would be surprised if this were a commonly understood reference. Note that it is about more than just a reference to bad workmanship, it is a reflection on the need for professional responsibility (although based on the context OP provided in a comment, it was probably just a macabre joke).