Preheat the broiler. Brush both sides of the bread with the olive oil and arrange on a baking sheet. Broil the bread slices about 10 inches from the heat for about 3 minutes, until golden on both sides. Rub the croutons with the halved garlic clove.
Melt the butter in a large, heavy saucepan. Add the bacon and cook over moderately high heat until browned, about 4 minutes. Add the minced garlic, corn, scallions and crushed red pepper and cook over moderately high heat, stirring frequently, until the corn is crisp-tender, about 5 minutes.
Stir in the flour and cook for 1 minute, until everything is coated. Add the clam juice, water and heavy cream and cook, stirring, until slightly thickened, about 4 minutes. Season with salt and pepper. Add the shrimp and simmer until just pink and cooked through, 3 to 4 minutes. Stir in the vermouth.
Put the croutons in deep bowls, spoon the shrimp and corn chowder on top and serve.