Arriving at an airport one day, Bernstein was asked by a photographer if he would mind posing for a picture astride a motorcycle. Bernstein objected. "I don't ride a motorcycle," he said. "It would be phony." The photographer tried to persuade him. He showed him the controls, explaining briefly how to operate them. "I'm sure you could ride it if you tried," he said encouragingly. Bernstein climbed onto the machine and, to the horror of his colleagues, shot off at top speed across the airfield. After a few other maneuvers he returned, grinning broadly. "Now you can take your picture," he announced. "I'm a motorcycle rider."
Here's another one that I also thought was funny.
Bernstein's father was criticized for not having given his talented son more encouragement when he was a child. He protested: "How was I to know he would grow up to be Leonard Bernstein?"