Great thread Wen,
One of my favorite movies is "Dr. Strangelove". There is a scene where Peter Sellers, playing Dr. Strangelove, is addressing the President and the Joint Chief's about surviving a nuclear war. During his monologue you can see the Russian Embassador standing to the left clearly cracking up at Sellers' routine.
There is also an obvious vocal overdub when Slim Pickins says "A fella coud have a pretty good weekend in Vegas with all that stuff". The orginal city was Dallas, but the line had to be changed because of the (then) recent assassination of President Kennedy.