In a heavy skillet, heat the butter over medium-high heat until melted and sizzling. Add the onion, bell pepper, and garlic and sauté until softened, about 3 minutes.
Stir in the thyme, red pepper flakes, black pepper, salt, sugar (if using), and corn. Cook, stirring, until the corn is cooked through, about 5 minutes.
Add the cream and cook 5 minutes more to thicken. Stir in the parsley and green onions. Taste and adjust seasoning with more salt and pepper.