Try the Russian food at State of the Union. After way too many glasses of wine and not just a few vodkas, a friend and I threatened to steal the statue of Lenin off of the bar one night. They said that if we could lift it we could take it. It is still there. You will find jazz and coffee, and rock and retro, and drinking places of all sorts.
Crowds tend to be young and mixed, straight and gay, all races, men and women.
Places are scattered, but stay open late. If you don't know the area, after dark stay west of 15th Street and take a taxi back to your hotel. There are ethnic restaurants galore. The Metro is a walk, so take a cab. Have them drop you off at the corner of 18th and Columbia Road and walk from there.