haha. i just thought because they are in 2 different leagues and "share" (I use that term loosely) MASN maybe there was no real rivalry. guess i was wrong. lol
No worries. But yeah, as others have since alluded to... Any true Washingtonian possesses a deep hatred of all things Orioles. Nothing to do with the team, but the jackass owner who kept baseball out of DC years after it should have returned (the expansions during the 90s.)
Add that to the Nats getting further screwed by Angelos with the MASN deal, some folks in the area viewing Baltimore with derision and scorn as a crime ridden craphole (Folks who haven't been across the Anacostia in DC... Glass houses and stones.) The moronic "MASN cup" has the teams attempting to create a rivalry based on the actual teams and games, not political/soclial BS. Largely a failure, again as others have mentioned, the NL/AL division prevents any true rivalry as with the Phillies.
The two teams are far enough apart there isn't the Mets/Yankees or Cubs/Sox type of hatred. DC folks don't identify with Baltimore in any way, shape or form. In football, there are Redskins fans that are Washingtonians, and Ravens fans that are Marylanders. Again, due to NFC and AFC separation, there's little to no Skins/Ravens rivalry. Heck, they made the Super Bowl and this area largely didn't give a crap.
But so long as Angelos owns the team, the majority of Nats fans will despise/hate the O's franchise.