The Lesser Known Feynman - Juval Ne-eman

In one sphere, at least, Feynman made a deliberate effort to play the role of enfant terrible. Combining his love for scientific truth and his hatred of "impostors," he was always willing to play cat- and-mouse games to expose flaws and pretense - all of which made him the terror of lecturers who came to Caltech to present their intellectual wares. On my first visit, I gave a series of ten lectures on "group theory," the mathematical apparatus I used, and Feynman interrupted me with questions every 3-4 minutes. I knew the material, however, and in the end it was Feynman who got tired out. On the other hand, I remember the visit of a well-known Swiss physicist, Johann Jauch, who after half an hour of torture, flung the chalk away, announced he could not go on this way, and walked out the door.

In 1976, Werner Heisenberg, one of the leading physicists of the 20th century, made a stop at Caltech as part of a cross-country lecture tour. Since 1950, he had been expounding a certain theory that was generally acknowledged as worthless. Out of respect, however, people usually refrained from arguing with him. His lecture at Caltech was on this theory. Gell-Mann stayed away purposely, but Feynman was there and made his presence felt. At a certain point he got up and shouted: "If that's so, your theory is crap." Mortified, Heisenberg left the hall, and according to the distinguished physicist Harald Fritzsch, who was at Caltech at the time and on close terms with him, he never recovered from the shock. He died that same year.

But there was someone who gave Feynman a taste of his own medicine. The Norwegian-American physicist Ivar Giaever once suffered through a lecture with Feynman. Two years later, he came back to Caltech to give another lecture. This time, however, Giaever not only answered Feynman to the point, but made him look stupid. Obviously, he had done a good job of preparing ahead, deliberately slipping in remarks to provoke Feynman - who walked straight into his trap. Everyone in the lecture hall could feel how stunned Feynman was.

From : http://www2.physics.umd.edu/~yskim/feynman/yuval.html