Good Happy hour bar - lively crow of 30 somethings and decent bar food
Bourbon Glover Park (2348 Wisconsin Ave. NW)! Great crowd of regulars in their late 20s and mid-30s, neighborhood vibe, more than decent bar food. $2 off drafts M-F 5-7:30pm; 1/2 price wine, Willett bourbon, and 750ml bottles of beer on Wednesdays, fried chicken special on Thursdays, and $6 Manhattans on Fridays. One of the few places you can get a very good beer for $3 in the city.
Full disclosure: I work here. But I would go here even if I didn't.
My favorite happy hour spots are Oyamel, which features $5 margaritas and sangria and 2 for $5 taco specials. It goes from 4-7, which is nice for those of us that can't leave work early. Also, The Source has an Izakaya menu from 4-6pm, which is 3 for $20 small plates. Unfortunately, no drink specials. The pork belly bao buns though make the $10 drinks worth it!
Poste is also good, especially in the nice weather months, when you can sit outside.
Liberty Tavern although it is packed and there might be a 50/50 20 something to 30 somethings ratio, Lyon Hall, Restaurant 3, Boulevard Woodgrill, Eventide, Eat Bar.
In DC: Zaytinya, PS7, Poste especially when the weather is nice.
777 I Street, NW, Washington, DC 20001
701 9th St NW, Washington, DC 20001
2950 Clarendon Blvd, Arlington, VA 22201
The Liberty Tavern
3195 Wilson Boulevard, Arlington, VA 22201