In The Maestro, Elaine tried to explain that Leonard Bernstein was probably known as "Lenny" to his friends. But Bob Cobb insisted that they called him "maestro," and therefore everyone should do likewise for him.
Update: contrary to this humorous plot element, the truth was revealed in Sunday's Los Angeles Times, when several letters commented on a feature story about Bernstein that appeared in the October 10th edition of the paper. One of the writers told of taking a course from him at MIT in 1956. When his students asked what title they should use in addressing him, he replied that they should simply call him "Lenny."