I know the concerto well. Once a new conductor at concert time decided to conduct in 2-4 instead of 4-4 to give it some spontaneous energy but the orchestra instead thought it was 4-4 so they played it twice as slow. When the soloists joined in they too went at a lugubrious molassas tempo. There was no hope so I stood up and did my best Jimmy Durante imitation and yelled "Stop the music, stop the music... Now lets play the hell outta this thing, Maestro" then the conductor did a furious 4-4 and we began again. Most people thought it was part of the act.