An action sequence was to be shot with some cars chasing 'John Abraham'. Unfortunately, at the time of shooting, Abraham's mother was crossing the road and she presumed he was being attacked and freaked out. Shooting was halted while Abraham calmed his mother and reassured her it was only a film shoot.
The trivia items below may give away important plot points.
The number 9211 in Hindi word form becomes Nau-Do-Gyaara (9-2-11), which is a Hindi-lingual idiom meaning "to run away". An apt title, as it's the number of the taxi around which the whole movie revolves around, and it is the solution the two main characters have for their problems. The number was conceived by publicity designers while they were designing the film posters. They suggested it to director Milan Luthria and he liked it - he said it matched the Tom-and-Jerry spirit of the film.