The orioles are a garbage franchise in a garbage city, and we would not dignify them with a rivalry. However, most of us do hate them, but that's because they kept baseball out of DC for 30+ years.
This. But beware of birds fans in Nats gear (we have some undercover ones here who showed themselves last year when the birds made the playoffs but they will probably go back in "hiding" and even trash talk the birds when they drop back down to the cellar).