My favorite scene is on ANH, where Obi-Wan and Luke/Han are about to split up. Han calls Obi-Wan a fool, and Obi says "Who's more foolish, the fool or the foo who follows him?". Han replies, "D*** it old man, I knew you were going to say that."
"Why do I feel that you're going to be the death of me someday?" - Obi-Wan Kenobi to Anakin Skywalker, Attack of the Clones