Preheat the oven to 350°F. Lightly coat a 13 x 9-inch baking pan with nonstick cooking spray; optionally line with foil for easier removal and spray the foil.
In a food processor, pulse the graham cracker crumbs, powdered sugar, and 2 tablespoons peanut butter until well combined. If you don't have a processor, mix in a bowl until evenly combined.
Stir the melted butter into the graham mixture until evenly moistened, then press the mixture firmly into the bottom of the prepared pan to form the crust.
Place 1/4 cup peanut butter in a microwave-safe bowl and microwave about 15 seconds, or until softened and stirrable. Stir the softened peanut butter into the sweetened condensed milk until smooth.
Pour the sweetened condensed milk and peanut butter mixture evenly over the crust.
Layer the chocolate chips, peanut butter chips, mini peanut butter cups, and flaked coconut evenly over the condensed milk layer, then press the toppings gently with a fork to help them adhere.
Bake for 25 to 30 minutes, or until the top is lightly browned. Remove from the oven and loosen the edges while still warm, then cool completely on a wire rack.
If you lined the pan with foil, lift the bars out using the foil edges and cut into bars or diamonds once cooled.