Prepare pineapple: trim outside of pineapple off, core and slice into rings.
Toast coconut: Place coconut in large skillet and toast over medium-medium high heat until golden. Remove and set aside.
Prepare rum sauce: In small saucepan, bring rum and brown sugar to boil, then reduce heat and simmer to reduce. Add vanilla and butter. Let cool.
Cook and assemble: Brush pineapple slices with rum sauce. Grill pineapple slices to heat and obtain nice looking grill marks. To serve, place one pineapple slice on plate. Top with scoop of vanilla ice cream, drizzle rum sauce over ice cream and sprinkle with toasted coconut. Top with a cherry, if desired.