It is difficult to describe general characteristics of Washington D.C. residents, due in part to the transient nature of much of the population. Few people you encounter, it seems, are actually natives of Washington. People from other parts of the United States, or the world, far outnumber those born in the metro area.
Some traits can be loosely applied to residents of the different metro areas, considering it encompasses two states and the District of Columbia. Virginians tend to be more conservative than Marylanders, and also less involved in the political goings-on in Washington. Residents of Washington proper tend to be younger and often faster paced than their neighbors.