From this Guardian piece, pointed out to us by BoingBoing:

In 1987, he was invited to a White House dinner by Ronald Reagan. Few of the guests appeared to know who he was. During dinner, Nancy Reagan turned to him and asked what he’d done with his life to merit an invitation. Straight-faced, Davis replied: “Well, I’ve changed the course of music five or six times. What have you done except fuck the president?”