excuse my french

Also 'Pardon my French.' Phrase mumbled insincerely immediately after or before one swears a blue streak within earshot of the elderly, the young, or the simply uptight.

Pardon my bad language, or forgive me for swearing.

Something soccer moms often say before, after, or in between swearing, as if to convince someone that they are speaking to that they have picked up a foreign language, and are not just using words like fuck, shit, ass, bitch, or possibly Barbara Steisand.

1. To pardon one's self of foul language.
2. To pardon one's self of going against the grain of social establishment, political correctness, fundamental beliefs, or popular culture.

French is commonly associated with sexual vulgarity. The idea that anything French is wicked, sexual, and decadent has invited many English speakers to insult the frogs.
The term "French" has many other sexual meanings. French culture is a common sex worker euphemism for oral sex, a French lesson is a visit to a prostitute, French kissing is a more vulgar kind of kissing. They used to call porn pictures "French prints" and being Frenchified was catching syphilis.
Reference: The Slanguage of Sex by Brigid McConville & John Shearlaw, 1985.

What people sometimes say when they accidently swear.

Said to someone after using a bad word.