After Harry's first Divination class, Professor McGonagall said that ---.

From the text:

“Really, what has got into you all today?” said Professor McGonagall, turning back into herself with a faint pop, and staring around at them all. “Not that it matters, but that’s the first time my transformation’s not got applause from a class.”
Everybody’s heads turned toward Harry again, but nobody spoke. Then Hermione raised her hand.
“Please, Professor, we’ve just had our first Divination class, and we were reading the tea leaves, and —”
“Ah, of course,” said Professor McGonagall, suddenly frowning. “There is no need to say any more, Miss Granger. Tell me, which of you will be dying this year?”
Everyone stared at her.
“Me,” said Harry, finally.
“I see,” said Professor McGonagall, fixing Harry with her beady eyes. “Then you should know, Potter, that Sybill Trelawney has predicted the death of one student a year since she arrived at this school. None of them has died yet. Seeing death omens is her favorite way of greeting a new class. If it were not for the fact that I never speak ill of my colleagues —” Professor McGonagall broke off, and they saw that her nostrils had gone white. She went on, more calmly, “Divination is one of the most imprecise branches of magic. I shall not conceal from you that I have very little patience with it. True Seers are very rare, and Professor Trelawney…”