Director - Woody Allen

Neurotic Jewish comedian Alvy Singer (Woody Allen) is at a party when his friend passes him a small tin filled with cocaine. As Alvy takes the tin in his hands he has a violent sneeze - sending white powder everywhere. The surrounding actors’ uncontrollable laughter was spontaneous and genuine and Allen decided to leave it in the final cut of the film after it tested well with audiences.
So one of the most famous sneezes in cinema history was never actually intended to be part of the final film - it actually occurred during a scene rehearsal.