I would nominate “Frankly my dear, I don’t give a damn.” from you-know-where, but since it was lifted from the book, (except for"frankly") I’m going to go with a different choice.
Therefore, I nominate this famous scene from the first National Lampoon’s Vacation.
Chevy Chase’s finest cinematic moment. A performance that surely brings back vacation memories for most of us.
Any other nominees?