First day on the job, the musicians had already studied the scores for the upcoming performance and they started rehearsing. The director would interrupt the orchestra as usual during the rehearsals to give instructions from time to time.
But his advises didn't make much sense, and his hand signs looked more like a layman enjoying the music rather than a director making the orchestra keep up with the tempo. The musicians began to suspect he wasn't very bright and were sharing these views between them at a low voice.
Until one of the percussionists got sick of all that nonsense. He took the drumsticks and hit the timpani as hard as he could, making a LOOOOUD bang that scared the whole orchestra.
After everyone recovered from the initial confusion, the director said "Very funny, huh? Who of you did it?"