I first heard this story when I was an undergraduate at Columbia University in the 1970s. I have no idea whether it is true or apochrypha, but it sounds entirely plausible.
Professsor Sidney Morgenbesser, distinguished professor of philosophy at Columbia University, sat at the back of a philosophy seminar while a graduate student delivered a paper on Double Positive Statements. The student’s thesis was that while there are many examples of double negatives meaning a positive; there are NO examples of double positives meaning a negative.
>From the back of the room came Prof. Morgenbesser’s booming response, “Yeah, Yeah!”
I imagine the student fled the room in shame.
UPDATE: Professor Morgenbesser has died at the age of 82. The New York Times obituary provides the orginal source for the above story and adds a few tremendously witty and funny stories to the treasury of Morgenbesser wisdom in Sidney Morgenbesser, Kibbitzing Philosopher, Dies.