My backwards brain at work again ... to myself, it's usually a city name, but not necessarily the city of the airport.
ARN is usually 'Stockholm', rather than Arlanda.
BWI is 'Baltimore'.
IAD used to be 'Dulles' to me, but after confusing my Mom, I call it 'Centreville'.
DCA is 'DC'. Not National, not Reagan, 'DC'.
EWR is 'Newark not New York'. Yup, the whole thing.

I sometimes am not clear when I speak (as if anyone here had not already noticed that ) so because of that, when speaking to friends and family, I've taken to the three-letter codes and speaking each letter when helping them do routings. I'll still speak the closest city name as we start the conversation, but it's three-letter codes once the city decision has been made.
I still confuse my Mom a little, but bless her, she tries to keep up with my insanity.