Could you please tell me the meaning of "the supercilious assumption was that" in the following excerpt of the second chapter of The Great Gatsby?
I think he’d tanked up a good deal at luncheon and his determination to have my company bordered on violence. The supercilious assumption was that on Sunday afternoon I had nothing better to do.
A supercilious person is one who believes he is better or more important than other people. Early on in Chapter 1, Nick describes Tom in this way:
Now he was a sturdy straw-haired man of thirty with a rather hard mouth and a supercilious manner. Two shining arrogant eyes had established dominance over his face and gave him the appearance of always leaning aggressively forward.
Tom definitely thinks he is better than others. This is clear in how he treats Daisy, and certainly how he treats Myrtle and George. But even in broader terms, Tom believes that his (white) race is superior to other races. He reveals his racist attitude when he mentions the book The Rise of the Colored Empires. He says to Nick, Daisy, and Jordan that, “This fellow has worked out the whole thing. It’s up to us, who are the dominant race, to watch out or these other races will have control of things.”
Tom is arrogant and proud. He is definitely supercilious. When Tom takes Nick to meet Myrtle, Tom thoughtlessly assumes that Nick has nothing to do that afternoon. In other words, Tom is so full of himself that he assumes that Nick would rather spend time with him than with whatever he had or had not planned for that afternoon.
In the extract, Nick implies that Tom Buchanan, a character he does not like much and husband of Daisy, his cousin, is a bit drunk. This, in itself, seems to bring out the worst in Tom.
Referring to Him as supercilious means that Nick believed that Tom thought himself better than others. He looked down on other people and was arrogant. Tom's attitude was informed by his wealth. He believed that having so much money automatically implied that he was better than everyone and that his opinion was more important and had more value than that of anyone else.
It is for this reason that Nick believes that Tom's assumption that he (Nick) had nothing better to do on a Sunday afternoon than visit Tom's girlfriend, Myrtle Wilson, is offensive. It is as if Tom just expects Nick to acquiesce to his request, since he is convinced that, he is after all, better than Nick and knows what's best for him.
Furthermore, Nick means that Tom, because of his conceit, does not even bother practising courteous social skills. He does not ask Nick to accompany him, he demands it, as if he has a right to do so. It does not even cross his mind that Nick might have something better planned for the day. As Nick states:
... he ... literally forced me from the car.
“We’re getting off,” he insisted. “I want you to meet my girl.”