How to Make It
Split the vanilla bean in half lengthwise using a sharp paring knife. Run the dull side of the knife blade down the length of each half, scraping up the seeds. Combine the seeds and sugar in a large bowl.
Cut away the peel and pith of the grapefruits; slice into rounds and transfer to the bowl with any juices. Add the raspberries and mango and toss to combine. Let stand for 10 minutes. Garnish with the mint, if desired.