Melt the butter in a sauté pan over high heat. Add pineapple chunks and sauté until slightly brown. Add sugar and continue cooking a bit more. Add rum, flame, and cook until the rum is mostly evaporated.
Fold a crêpe into quarters and place on a warmed serving plate. Lift the top edge of the crêpe and spoon part of the pineapple mixture into the crêpe. Place the plate in the oven to keep warm while the second crêpe is filled in the same manner.
In the meantime, deglaze the sauté pan with the pineapple juice. Boil until reduced and divide over the crêpes. Sprinkle the crêpes with the grated coconut [optional]. Serve immediately.