Preheat the oven to 350 degrees F.
To make the pie crust: In a resealable plastic bag, crush the graham crackers. Transfer the crushed graham crackers into a big bowl and mix in the grated dark chocolate shavings, brown sugar, and melted butter. Line 6 (4-inch) mini pie molds with the crust mixture, making crust about 1/8-inch thick. Bake for 8 to 10 minutes, then cool.
To make the filling: In a bowl, combine egg yolks, fresh pink grapefruit juice, fresh lemon juice, pink grapefruit zest, and lemon zest. Mix and set aside. In a heavy saucepan add: brown sugar, cornstarch, a pinch of sea salt, and water. Bring to a boil over medium heat whisking constantly for 2 to 3 minutes, until the mixture thickens. Slowly whisk in a small portion of this mixture to the egg yolks-citrus mixture. Cook's Note: Be careful not to cook the yolks.
Whisk the egg yolk-citrus mixture back into the pot, reduce the heat to low, add 2 tablespoons unsalted butter and whisk for 8 more minutes, until very thick. Cover and refrigerate the mixture for 3 hours.
Preheat the oven to 375 degrees F.
To make the meringue: In clean bowl, combine the 4 egg whites, white sugar, and white vinegar. Using electric mixer or whisk, whip until stiff peaks form.
Evenly divide and spoon the chilled citrus filling into the graham cracker crusts and top with lots of meringue. Bake for 10 minutes, or until the meringues brown slightly.