I just watched Chamber of Seacrets on TV and I had to add this one from right after Lochart's memory charm backfires
Lockhart: um, who are you?
Ron: I'm Ron Weasley
Lockhart: Oh, well, and um, who am I?
Ron: You're Professor Lockhart
Lockhart: *pause* Well this is an odd sort of place. Do you live here?
Ron: No. *slaps lockhart across the back of the head*