I don't know if this look is specific to the DC area, but last night strolling through Georgetown we saw a dude with his long-sleeve, button up shirt half tucked in.
By this I mean one side was tucked in, the rest of the shirt was hanging out.
Is this the new polo collar up?
Is this the "on the fence" of the corporate-casual set?
Does the side your shirt is untucked on signify where you hang?