"Hey, city boy. Try some of these rocky mountain oysters!"
"Why, these oysters grow in freshwater streams in the Rocky Mountains, of course! Very rare, a tasty delicacy."
Oysters are a marine bivalve mollusk. The Rocky Mountains are a mountain range in the western USA and Canada. The Rockies are well known for their lack of proximity to coastal waters. In summary, no species of oyster are native to the Rocky Mountains.
Thus, the trickery of the Rocky Mountain Oyster. Almost from the same school of thought as a shelf-stretcher, light-bulb repair kit, or a snipe hunt, the concept of a rocky mountain oyster is used nearly exclusively to embarrass or patronize a greenhorn, FOB, or n00b.
Unlike the previously mentioned shelf-stretcher and snipe hunt, a rocky mountain oyster has a real world counterpart. The actual comestible, though, is not an oyster. In fact, it is not seafood, though at one time it did produce swimmers.
Rocky mountain oysters are testicles. Usually from cattle, though on rare occasions sheep and even horse testicles have been used as well. Just about any animal testicle recipe has a corresponding name, but rocky mountain oysters are predominantly beef. A young bull, in the process of becoming a steer has its testicles removed by a veterinarian, rancher, or cowboy. People (such as Mr. T) then prepare and eat them.
You might ask yourself, "Why would anybody in their right mind, given other choices of cuisine, eat testicles?"
Well, people have been eating balls for a long time. Eating a virile animal's nuts was regarded as a fertility treatment as early the Roman Empire, possibly even earlier. Teste consumption has base in Asian cultures as well. In modern times, the willingness to eat a bull's balls can be seen as a sign of toughness or masculinity. This is especially true in the American west, where the "Rocky Mountain" part of the name comes from.
Once the testicles are separated from the previous owner, they are prepared, usually with a slight seasoning, and cooked in any number of ways; fried, boiled, and even raw. Aliases for this exotic domestic dish include cowboy caviar, Montana tendergroin, swinging beef, prairie oysters, and calf fries. There are probably as many names for rocky mountain oysters as there are recipes, but for example's sake (and because this is a food node), here is a recipe.
Rocky Mountain oysters are available at many fine restaurants in the western USA and Canada. They are also (somewhat famously) sold at a concessions booth in the stadium that is home to the Colorado Rockies baseball team.
2 pounds calf testicles*
2 cups beer
2 eggs, beaten
1 ½ cups all-purpose flour
¼ cup yellow cornmeal
Salt and ground black pepper to taste
1 tablespoon hot pepper sauce
* Be sure to ask your butcher for calf testicles, not bull testicles. Calf testicles are the size of a walnut and are much more tender than the larger bull testicles.
** Use enough vegetable oil to fill your frying container halfway to the top (to allow for bubbling up and splattering) and to completely cover calf testicles while frying.
With a very sharp knife, split the tough skin-like muscle that surrounds each testicle. Remove the skin (you can remove the skin easily if the testicles are frozen, then peel while thawing). Slice each testicle into approximately ¼- to ½- inch-thick ovals. Place slices in a large pan or bowl with enough beer to cover them; cover and let sit 2 hours.
In a shallow bowl, combine eggs, flour, cornmeal, salt, and pepper. Remove testicles from beer; drain and dredge thoroughly in the flour mixture. In a large, deep pot, heat oil to 375 degrees F. Deep fry 3 minutes or until golden brown (will rise to the surface when done). Drain on paper towels. Serve warm with your favorite hot pepper sauce.