You may have enjoyed the featured dish at D.C.’s 5th Annual Rocky Mountain Oyster Festival, put on by the Montana State Society Saturday night. You may have. Rocky mountain oyster; prairie oyster; calf fries; cowboy caviar; Montana tendergroins; swinging beef. No matter what you call them, it’s hard to step around what they really are: breaded and fried slices of cow/bull testicles. Yet how many of the several hundred 20-somethings shelled out $20 for the…