I have not attempted to fly out of the wrong airport, but I did once make a rental car reservation at the wrong airport: Reykjavik instead of Keflavik. One would -- this one would, anyway -- think that Reykjavik would only have one airport, because it is so small, but it has two, and the international one is Keflavik, not Reykjavik.

Fortunately there is a shuttle bus between the two.