^^ When I was in college, I went to my cousin's wedding in Naples. It was in January, I think, or sometime around there. The weather was about 60-ish. His wife's parents had a summer house that was apparently only a few doors down from one of Bill Gates' house... it was unreal. But I was amazed at how early the bars and everything closed around there!
Everyone, come to DC! Whereas some magazines will tell you to go to places like Ben's Chili Bowl for something off the beaten track, that is ridiculous.
Do a Segway tour of the mall and Capitol. You get cute little helmets and everything.
Take a late-night haunted tour of Old Town, Alexandria.
Check out
http://www.internationalclubdc.com/Events/Default.aspx for listings of events held in embassies! For instance, learn to dance the waltz and salsa in the French Embassy and have a wine reception there.
Visit the PX in Old Town or the Gibson at 14th and U for a "speakeasy" type of night- they create drinks to suit your mood and make everything from scratch (except the alcohol, of course).
See the Nationals play... oh wait, they suck and lose every game. BUT, it is a pretty new stadium, with cheap tickets (as no one wants to watch the crappiest team in all of MLB).
There are a million other things to do, and the ones I mentioned aren't even that good. Forgive me, I'm in a sinus headache haze.