Leonard Bernstein
The first great conductor to be wholly educated in America. Although he did great at the Curtis Institute in Philadelphia, he only did OK as an undergraduate at Harvard. Part of the problem was that although his talent was obvious, if he wasn't interested in a class, he'd blow it off. And as one teacher said, they didn't give grades on talent, but whether the student did the work.
When taking a course in counterpoint, Lenny skipped most of the classes and showed up at the end of the term with this compositon. After hearing it, the professor said (with surprising courtesy) that it had little to do with what they had been studying all semester. Lenny then slammed the piano and yelled, "Well, I like it!"
Lenny got his "C".