Infamously, Nikolay Rubinstein dismissed Tchaikovsky's First Piano Concerto as unplayable and ill-composed. And this, to make the pill all the more bitter, was done directly after the composer had performed the freshly finished piece for the pianist. Rubinstein later apologized for his reaction and helped to cement the concerto's place in the repertoire by performing it himself.
Tchaikovsky dedicated his Second Piano Concerto to Rubinstein, who was to premiere the work. Unfortunately the pianist died before completion.