"If I really wanted to, I could find out the temperature of your ass when I disguised as that armchair."
Dumbledore: "I'd like to present our new Potions master, Horace Slughorn."
[Harry and Ron share confused looks as they thought he was the new DADA teacher.]
Slughorn: "Well what did you think I was going to be around here, a fucking night watchman?"
"Eat your g-damn oatmeal, you little shit, it's Quidditch today. You need the horsepower."
"No pumpkin pasties! Makes me fart!"
To Cormac McLaggen after listening to him run his mouth: "Will you listen to this guy? He'll be chasing them dogs 'til his dick runs off."
And the best of all:
"You weren't just snoggin' Ginny in the hallway Harry, there were all sorts of intimate acts, oral and whatnot, that can be particularly hard for a trusting friend like Ron to forgive and IMPOSSIBLE to forget."