When Tom hits Myrtle in The Great Gatsby, he is revealed to be ignorant, abusive, unenlightened, sexist, egotistical, selfish, and a bully.
He is a patriarch of patriachs, dominating his male world at a whim. He sees women and those who are of a lesser social and economic class than he is as beneath him. He lives in a world that just recently allowed women the vote, and he behaves accordingly. He and his family (although he disrespects Daisy, also, when he is with her) are better than Myrtle and hers, and though he will have an affair with her, he will not tolerate her thinking she is an equal.