George's King of Falafel has been a late night Georgetown staple since my college days. http://washingtondc.menupages.com/restaurants/georges-townhouse/
Post-bar hopping it was the perfect place to stumble in and order one of their sandwiches like falafel, shish taouk, shwarma or shish kabob, or a decent cheesesteak before heading home.
These days I'm more likely to stop in George's after a yoga class for a quick bite. The guys working the counter are pleasant, and they assembled the sandwich pretty quickly. It's better when the falafel are freshly fried, and this is more Lebanese-style falafel than Amsterdam Falafel Shop or even Maoz's.