Ravel was very particular about how his works were performed.
Ravel always insisted that the tempo for Boléro should be moderate and rigorously maintained throughout. He made a recording of that, too establishing his requirement. Toscanini took it much faster and made an accelerando towards the end. Ravel, who was in the audience, objected. He refused to shake hands with the famous conductor, saying, “That’s not my tempo”, to which Toscanini retorted coolly: “When I play your tempo the piece is ineffective.” “Then don’t play!” was Ravel’s tart and uncompromising riposte. There some reconciliation later; but from then on Toscanini avoided Boléro.
James, Burnett (1983) Ravel: his life and times. New York: Hippocrene Books, p.128.