Oda drew two future versions of each Strawhat. One where everything works out as planned, another where somethign went wrong. Joyboy must have entered his bad timeline. He made a promise to the Fishmen. He didn't expect to lose. Yet he did. Imu Nerona seized world power. So Joyboy should look analogoues to bad timeline Luffy, meaning he was balding, obese and had missing teeth. Perhaps Roger found out about that on Laughtale, which is why he had to laugh so hard.
