Just a quick one:  Xcode 7.2 was crashing on me recently when I tried to delete an entity from the Core Data model.

It turned out to be some kind of issue with having the Core Data model open in another tab and set to show the graph view while deleting from the list view.

At first it was crashing when I had the list view in the main frame and graph view open in the assistant editor pane.  But it also crashed when the graph view was open in another tab.

If its crashing on you, just close the other tab or pane before deleting an entity.