Why did Jack hate Piggy? Why did Jack hate Ralph? Why did Ralph hate Jack? What is all this hate about?
You are probably in the very beginning of this wonderful book. The characters represent themselves and something beyond themselves--they are allegories.
Piggy, the one with the glasses and who expects everyone to follow the rules and to think before they act and to be civil, represents logic and reason. This is why Jack hates him. Jack is spontaneous and "fly by the seat of his pants". He doesn't want to live by rules...he's done too much of that already in his young life.
Jack hates Ralph because Ralph is Piggy's friend. Piggy is the thinker, and Ralph is the leader who carries out those ideas. Ralph also insists that the boys keep the fire lit, that they collect firewood, build shelters, collect fresh water for drinking...all of this translates to civilization and work. Jack wants none of that.
Ralph didn't hate Jack at first, and probably didn't at the end. Ralph resented Jack for forcing the other boys through lure of fun and games and later through fear to move from Ralph and Piggy's beach camp to Jack's cliff camp. Jack is also responsible for Simon and Piggy's deaths, and planned to kill Ralph as well. These are reasons for Ralph to dislike Jack.
Jack cannot stand Piggy because they have drastically different beliefs concerning civilization. Piggy emphatically defends civility, structure, and morality throughout the novel, while Jack is the epitome of barbarism and savagery. Jack also resents the fact that Piggy continually argues with him and is Ralph's biggest supporter.
Jack is jealous that Ralph was chosen as the leader and hates the fact that he initially does not have authority over the entire group of boys. Later on in the novel, Jack begins to hate Ralph because he views him as a threat to his authority.
Ralph opposes everything that Jack stands for and believes that Jack is a dangerous, reckless individual. Ralph begins to hate Jack when Jack refuses to follow through with orders. Ralph sees Jack as a malevolent instigator who encourages others to act like savages.
William Golding illustrates the struggle between civility and humanity's inherent wickedness through the characters' relationships. Piggy and Ralph represent civilization, while Jack represents anarchy and humanity's primitive nature. Their conflicting relationships are an allegory for mankind's struggle to oppress its savage nature.