Bring a large pot of water to a boil. Should be as salty as sea water. Add the greens and blanch, just until tender, about 3 minutes. Using a slotted spoon, transfer the greens to a colander and rinse with cold water. Drain well and coarsely chop the greens.
In a large skillet, heat the olive oil. Add the garlic and crushed red pepper and cook over moderate heat until the garlic is golden brown, but not burnt, about 1 minute. Add the greens. Cover and cook until the greens are heated through, about 8 minutes, stirring occasionally. Season with salt and pepper.
Cool to room temperature before adding the vinegar. Serve.
Note: May be cooked ahead and refrigerated overnight. Serve slightly chilled.