But for everyone else:
The most WRONG lines in HBP
The page references are from the British edition.
Page 65, just as Dumbledore discovers Slughorn's location
And without warning, Dumbledore swooped, plunging the tip of his wand into the seat of the overstuffed armchair, which yelled, "Ouch!"
"Good evening, Horace," said Dumbledore, straightening up again.
"There was no need to stick the wand in that hard," he said gruffly, clambering to his feet. "It hurt."
Page 67, after Dumbledore has introduced Harry to Horace Slughorn:
Slughorn turned on Dumbledore, his expression shrewd.
'So that's how you thought you'd persuade me, is it? Well, the answer's no, Albus.'
He pushed past Harry, his face turned resolutely away with the air of a man trying to resist temptation.
Page 77, Dumbledore's conversation with Harry
"It was cruel," said Dumbledore softly, "that you and Sirius had such a short time together. A brutal ending to what should have been a long and happy relationship."
"Harry, however, had never been less interested in Quidditch; he was rapidly becoming obsessed with Draco Malfoy."
Page 391, Ron's conversation with Harry
Ron, "You're getting a bit obsessed with Malfoy, Harry. I mean, thinking about missing a match just to follow him..."
Page 429, Harry attempting to enter the Room of Requirement
Harry, "I need to see the place where Malfoy keeps coming secretly"
Harry tried every variation of 'I need to see what Draco Malfoy is doing inside you.'
Page 509, Trelawney, on Snape
Trelawney: "the pushing, thrusting young man who was prepared to listen at keyholes."
Page 513, Harry's argument with Dumbledore
"Well, I don't!" he (Harry) said, as loudly as before. "He's (Snape's) up to something with Draco Malfoy right now, right under your nose, and you still -"
"We have discussed this, Harry," said Dumbledore, and now he sounded stern again, "I have told you my views."
"You're leaving the school tonight and I'll bet you haven't even considered that Snape and Malfoy might be up to -"
"To what?" asked Dumbledore, his eyebrows raised. "What is it that you suspect them of doing, precisely?"
"I... they're up to something!" said Harry and his hands curled into fists as he said it.
Page 515, Dumbledore's conversation with Harry
"I didn't -" mumbled Harry, a little abashed, but Dumbledore cut across him.
"I do not wish to discuss the matter any further."
Harry bit back his retort, scared that he had gone too far, that he had ruined his chance of accompanying Dumbledore, but Dumbledore went on, "Do you wish to come with me tonight?"
"Yes," said Harry at once.
"Very well, then: listen."
Dumbledore drew himself up to his full height.
"I take you with me on one condition: that you obey any command I might give you at once, and without question."