Why does Sir Toby believe that he can act as he wishes in Olivias house?

Sir Toby likes to party and womanize. He does not want to be held responsible for what he does. He is Olivia's cousin and he uses her to get away with his antics. Sir Toby thinks that he embodies the theme of merriment, party and basically excess during Twelfth Night. He feels that this gives him licence to act like a brute.