As a French man living abroad, I often hear non-French people saying "Oh la la !" (along with an imitation of a kind of posh attitude) after someone talked about something that is typical of France or French people. I have been told that this expression is supposed to be typical of what French people say, which according to my experience is not really the case (this blog article is going in that direction as well).
Have there been specific elements of French movies, books or any exported culture trivia that made English-speaking people think that "oh la la" is something that French people actually say all the time, or that would explain why this phrase became a stereotype of the French language ?