Drain the crushed pineapple thoroughly in a fine strainer, pressing it lightly with a spoon to remove excess liquid. Set the pineapple aside while you prepare the filling.

In a large bowl, whisk the sweetened condensed milk with the fresh lemon or lime juice until blended and slightly thickened. The citrus juice reacts with the milk and creates the creamy base for the pie.

Stir in the drained crushed pineapple, sweetened shredded coconut, coconut extract, and optional rum extract. Mix just until the ingredients are evenly distributed.

Gently fold in the thawed whipped topping with a spatula. Use a light folding motion and avoid overmixing so the topping stays airy.

Spoon the filling into the prepared 9-inch graham-cracker crust. Smooth the top without pressing down heavily.

Cover the pie and refrigerate for at least 4 hours, or until firm enough to slice. Overnight chilling is preferable because the coconut absorbs some moisture and the flavor becomes more developed.

Add whipped topping, toasted coconut, pineapple pieces, or maraschino cherries immediately before serving. Slice with a clean knife and serve cold.