When the speaker isn't being sarcastic, "set" sort of means having what you need, or being ready, as in "I'm all set to go on my hiking trip", or "These boxes are all set for shipping." But in this context the girl is being ironic - she's saying that she has no need for the present, but from the angry way she says it, it is clear that what she really means is that she doesn't want the present because it's cheap. Does that make sense?

'I'm all set' A phrase used in place of I'm ok, I'm ready. To be satisfied and not need anything.

Hmm...Do you quite sure you didn't misheard? Maybe 'I'm sate' or something else ? Otherwise I reckone there's some kind of double meaning.

Hi Joseph, The word "set" has more definitions than any other word in the English language, according to the Oxford dictionary around 500. That doesn't include the slang definitions! I can think of two explanations that fit your question. The first comes from the idiom "set for life": To be set for life means to have enough money or supplies to last for the rest of one's life. By analogy, if someone asks you if you would like to buy a magazine subscription, you can answer with the slangy "No thanks I'm set for magazines." This means, as others have mentioned, that you have all the magazines that you want or need. "Thanks, I'm set" would make sense in that context. Another explanation that fits comes from the restaurant community. In an eating establishment the waiter sets the table properly, sets the plates of food before the customer, sets drinks on the table, and inquires about the customer's needs and desires. The manager of a restaurant might ask a waitress or waiter in business slang if their customers are 'all set'. It means: Have you done everything possible to satisfy the customers' needs? The customer might also use this expression in the following situation. When the waiter asks whether there is anything else the customer would like, dessert, another drink, etc., the customers can reply, "No thanks, I'm all set." This is equivalent to saying, "No thanks, I'm good"....or "No thanks, that's all for now." It is a way of refusing further service that the waiter will understand in most parts of North America. "Thanks, I'm set" is a way of refusing an offer. The girl in the sitcom by refusing the offer in this impersonal businesslike manner is indicating the lack of a close personal relationship between the man and herself. If someone were to refuse a serious offer or gift from a friend or potential bussiness partner in this slangy manner, it would show a lack of respect.

That´s a very good explanation.