Sphyracephala brevicornis. Rock Creek Park, Washington, DC, USA. 5 July 2014.

Not quite as impressive as its tropical cousins, but I still did a double-take when I realized what I was looking at. Please, please, please, let me take a couple of decent shots before you fly away! Only when I looked at the pictures later did I realized that she couldn't fly because she had a malformed wing. Definitely the Diptera sighting of the year.