Fill a large pot with enough water to reach a depth of 2 inches and bring to a boil. Add the bok choy and cook, stirring, for 1 minute; drain and rinse with cold water.
In the same pot, melt the butter over medium-high heat. Add the scallions and garlic and cook, stirring, until softened, about 2 minutes. Stir in the soy sauce, crushed red pepper and shrimp and cook until opaque, about 2 minutes. Stir in the bok choy until heated through, about 2 minutes.