Preheat the oven to 350 degrees F. Line a regular cupcake or muffin pan with 12 cupcake liners.
Sift the flour, baking powder, salt, 1/4 teaspoon black pepper and cayenne pepper into a medium bowl. Set the bowl aside. In a small bowl, combine the tomato juice, 1/4 cup vodka, lemon juice, hot sauce and Worcestershire sauce. Set the bowl aside. In the bowl of an electric stand mixer with a paddle attachment, cream the butter with the granulated sugar and horseradish sauce, about 5 minutes. Scrape down the sides of the bowl, and then add 1 egg at a time, scraping down the sides of the bowl after each addition. Turn the mixer to the lowest speed and add the flour and tomato juice mixtures, alternating between the two, beginning and ending with the flour. Mix until just combined. Scrape down the sides and mix for 30 seconds.
Fill the cupcake liners three-quarters full with batter and bake until baked through, 15 to 18 minutes.
In a small bowl, combine the remaining 2 tablespoons vodka and remaining 1/4 teaspoon black pepper. Use a pastry brush to brush the vodka mixture over the warm cupcakes. Cool the cupcakes completely, about 30 minutes.
Put the Cayenne Pepper Buttercream into a pastry bag and cut 1/2-inch off the tip. Frost the cupcakes once they are completely cool. Top with your favorite sprinkles or decoration.
Sift the powdered sugar into a medium bowl. In the bowl of an electric stand mixer with a paddle attachment, cream the butter and celery salt together, about 1 minute. Then add the powdered sugar and milk, alternating between the two. Beat until combined. Scrape the sides of the bowl. Add the lemon juice, vanilla and cayenne pepper. Mix until combined. Then beat the mixture on high until light and fluffy, 5 to 6 minutes.