Preheat the oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking pan.
Combine cake mix, undrained crushed pineapple, the eggs, and ½ cup of the melted butter in a bowl. Beat with an electric mixer on medium speed 2 minutes. Spread batter evenly in prepared pan.
Bake in the preheated oven until a toothpick inserted in center has a few moist crumbs, 30 to 35 minutes.
Cool cake completely on a wire rack, about 1 hour.
Whisk together 1 cup powdered sugar, 1 tablespoon melted butter and 2 tablespoons of reserved pineapple juice in a small bowl. Whisk in additional pineapple juice, 1 teaspoon at a time to reach spreadable consistency. Drizzle and gently spread over cooled cake. Top with pineapple tidbits.
Beat whipping cream with an electric mixer in a medium bowl until it thickens. Add 1 tablespoon powdered sugar and the vanilla. Beat until the cream holds soft peaks.
Top each serving with sweetened whipped cream and coconut.
