Ravana's attitudes towards Lord Rama is one of arrogance and ego. Ravana is almost bewildered as to why Lord Rama does not fall at his feet in complete submission. Ravana is at a point where he is consumed with his sense of power and control. He feels an inflated sense of self that he is able to make the Gods cower in fear. Thus, Ravana fails to understand why Lord Rama does not immediately acquiesce to his demands.
Part of the reason why the attitude towards Lord Rama is so distinct and different is because both represent opposing notions of consciousness. Lord Rama represents righteousness, dharma, and a sense of control in one's being. Ravana is representative of indulgence, the personalized ego, and a lack of control. Everything in Ravana's world is excess. Lanka is his own playground, the Ashoka Grove in which he holds Devi Sita hostage is filled with the most beautiful of temptress women that Ravana has assembled to satisfy his indulgent lust. Ravana embodies excess and a sense of individualistic desire. It is for this reason that his attitude towards Lord Rama is one of disdain and a sense of disrespect. Ravana believes that the penance he has undergone has entitled him to be seen as premier and superior to all else. It is in this light that he cannot fathom why Lord Rama would even think to challenge him. Taking Devi Sita was something that Ravana believed was his entitlement as possessing so much in way of power and authority. For Lord Rama to refuse to acquiesce to this and even challenge him in Lanka was an affront to the level of power that Ravana thought he possessed.