In a small skillet over medium heat, toast the shredded coconut, stirring frequently, until golden brown. Remove and set aside.
In the same skillet, melt the butter. Add brown sugar and crushed pineapple (with juice), stirring to combine.
Let the mixture simmer gently for about 5 minutes until slightly thickened. Stir in the dark rum if using, then remove from heat.
Scoop vanilla ice cream into serving bowls or glasses. Spoon warm pineapple sauce over the ice cream.
Top with whipped cream, toasted coconut, and a cherry if desired. Serve immediately.