Bring a large pot of lightly salted water to a boil. Cook acini de pepe in the boiling water, stirring occasionally until tender yet firm to the bite, about 11 minutes. Drain and rinse well with cold water.
Beat reserved pineapple juice, milk, sugar, and pudding mix together in a large bowl for about 2 minutes. Stir pineapple chunks, marshmallows, mandarin oranges, whipped topping, crushed pineapple, and coconut into the bowl with the juice mixture carefully. Cover and refrigerate at least 5 hours to overnight.
