Emma, being now certain of her ball, began to adopt as the next vexation Mr. Knightley's provoking indifference about it. Either because he did not dance himself, or because the plan had been formed without his being consulted, he seemed resolved that it should not interest him, determined against its exciting any present curiosity, or affording him any future amusement. To her voluntary communications Emma could get no more approving reply, than, (Chapter 30)

I don’t understand why Mr. Knightley’s distaste for a ball in Chapter 30 is a dig at Emma’s desire to be seen as comparable in dancing to Jane Fairfax. Does he know Emma feels (Chapter 29) she need not blush to compare herself with Jane in dancing? Emma was vexed by Mr. Knightley’s indifference to the ball. This is a vexation she adopted because his attitude provoked her—it almost seems she wants to quarrel with him. It seems to me she had been attempting to inspire his curiosity about the ball, a hopeless business IMO, with her voluntary communications—I imagine stuff like won’t he enjoy watching the dancing and if she included anything about showing off her dancing skills with Frank Churchill, who Mr. Knightley does not think highly of, then I can see why she seems to have annoyed him further rather than inspired any enthusiasm. I thought Mr. Knightley was telling Emma you will have to find your happiness in the dancing rather than my admiration of it because he does not find dancing that interesting to watch and also probably because he will not enjoy watching Frank Churchill. (;D)