Heat oven to 450 degrees F. Remove the ends of the grapefruits to stabilize on the cutting board. Using a sharp knife, remove the skin and bitter pith from the flesh. Over a small bowl, hold grapefruit in 1 hand and carefully remove the segments by sliding the knife between the flesh and the membrane. Toss grapefruit pieces with brown sugar and vanilla and divide among 6 ramekins. In a large bowl, beat egg whites until light and fluffy. Add sugar and beat until meringue is glossy and holds stiff peaks. Top each ramekin with 1/4 cup of ice cream. Cover with meringue and bake until golden brown, about 7 minutes.
