In various areas of the map you can come across beach balls that you can bounce into the air. On Starfish Island (middle island where the mansion is located) go to the most eastern house and in the pool you'll find the beach ball.
Tap into the ball to send it in the air then allow it to bounce on your head a total of 5 times. It's a bit awkward to see so pushing your camera out furthest from you may help.