Jack does not like Piggy. Jack is prejudiced and he is a coward. He is prejudiced against Piggy because Piggy is an intellectual. Outwardly, Jack makes fun of Piggy's size and his social awkwardness. Inwardly, Jack fears Piggy's intellect because Jack suspects it is much greater than his own. Jack wants to be in control. He wants to be the dictator and a smarter boy might stop his drive to achieve that goal. Even though Jack says he doesn't want to give Piggy meat because Piggy didn't hunt or help in the hunt for the meat, he really just wants to punish Piggy. Since Piggy is the group's intellectual - the one who questions most of the decisions made by the boys and the one who asks crucial questions - he is the biggest threat to Jack's plans to gain complete control. Jack also resents the fact that Piggy likes Ralph who represents the opposite of Jack - reason and fairness.