Slice the orange that fits in the rim of a lowball or rocks glass into four 1/4-inch-thick rounds. Use your thumb or the tip of a paring knife to create a small whole in the center of each orange round.
Cut the second orange to create 4 thick wedges. These represent shark fins. Push each shark fin wedge into the center of an orange round.
In a large cocktail shaker filled with ice, add the tequila, limeade, lime juice and blue curacao. Shake vigorously and strain into 4 serving glasses.
Place a shark fin orange garnish into each serving glass, making sure the orange round rests on the surface of the drink.
Drizzle 1 tablespoon of the grenadine over each shark fin garnish. As it drips into the blue cocktail, it represents the blood of a shark attack. Serve immediately.