When some people curse, why do they say, "Pardon my French"?

Question

Where did this come from?
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Answer 1

It has been suggested that the French language is used because of the association of the French people with vulgarity, and that this euphemism is an example of Francophobia.

An innocuous theory is that when the English were looking around for a foreign language to put into the phrase "pardon my ...", the closest one and obvious choice was neighbouring French. Additionally, French was for a long time the most-spoken foreign language in the United Kingdom.

Some believe the expression may have come from 1950s intellectuals who were well-versed in French. In the fifties, cursing was considered to be a major taboo, so the speaker would actually curse in French to be more polite. In these instances, "Pardon my French" would refer to actual French.

Answer 2

Man! Good question. I just had a woman at a bar say "Pardon my French" and then she cussed like a sailor who has been out to sea for 6 months. I've been around a lot of people from France. They don't act like that or talk like that. I can't wait to see the answers here.