Unfortunately, I happen to be very fluent in French, and not the kind that they speak in Paris. My French is more along the lines of "[vile swear word]...oops, pardon my French."
This tendency has gotten me into some pretty embarrassing situations. When I was in my early 20s, for instance, I was driving one of my young nephews to the park when another driver cut me off so sharply that I had to slam on the brakes to avoid an accident. I won't tell you exactly what I said, but to this day, more than 20 years later, my nephew can still repeat every cringe-worthy word of it. Let's just say that I didn't win any Aunt of the Year awards for that one.
Strong language in my writing has occasionally become an issue as well. Obviously, there are some venues where it is verboten. Even I know better than to cuss like a sailor when I'm writing grants, white papers, academic pieces, and church newsletters.
But a few months ago, I was writing a case study and used the word "dammit" as part of a quotation. The editor asked me to please remove the profanity and, red faced, I did as she requested.