How is Ralph unfriendly to Piggy? Why is that important? Is Ralph an innocent person?

When Ralph and Piggy first meet, it is Piggy who is eager to gain Ralph's friendship. He volunteers a great deal of information about his previous life. He tells him about his Aunty and the candies he would eat; he also shares with him the nickname "Piggy" on the condition that Ralph not share it. But Ralph shares it as soon as the opportunity arises at the first meeting. This slight is perhaps the reason why Piggy voted for Jack as chief. But it certainly indicates that Ralph is not always "nice" to Piggy.

This, along with Ralph's great pleasure at wounding the pig, demonstrates that Ralph is not innocent. He values Piggy in a way that Jack does not and is kinder in his treatment of him, but also more than willing to point out his limitations. 

The final testament to Ralph's loss of innocence comes when the Naval Officer arrives and Ralph weeps for the very fact that he had now lost whatever innocence he had when they crashed on the island.