What type of bad behavior is Jack displaying in Lord of the Flies?
Cruelty to others (especially to Piggy and the Littl'uns), cruelty to animals, militant dictator behavior, and murder. Where would you like to start?
Cruelty to others: Jack consistently taunts Piggy and even turns many of the other boys against him. He cruelly steals Piggy's glasses so that his tribe can be in control of making fire, leaving Piggy virtually blind. Once Jack proclaims himself chief, he uses cruel punishment for going against him in any way. Jack has Roger beat one of the lilttle'uns as proof of his power.
Cruelty to animals: Granted, the boys need to eat. However, when the boys kill the mother sow, they leave the piglets to die without a mother to feed them. Jack and his tribe of boys do horrific acts to the dead sow, one of which is raping it with a spear.
Militant Dictator behavior: this goes along with the cruelty to others. Jack's word is law in his tribe. Anyone who goes against him are severely punished. He even tries to hunt and kill Ralph.
Murder: While Jack didn't actually push the boulder that killed Piggy (Roger did that), he is responsible nevertheless. Roger was a flunky acting on Jack's behalf.