Do you know what it means?
The answer to that question, if you're U.K.-based, is probably generational. "San Fairy Ann" is an expression that was born out of a gap in the English language, so what are its origins and potential meanings?
British soldiers in World War One soon found out their French counterparts had a phrase that resembled "it doesn't matter" but that sounded much more satisfying, dismissing a problem out of hand. The expression was "Ça ne fait rien" and was anglicised into "San Fairy Ann". Google searches for the term often focus on this origin, labelling it "soldier slang". However, its use became far more widespread than that.
After the war, solders' return to civvy street meant that "San Fairy Ann" entered the general vernacular. For me it brings to mind my Nan's visits when I was a young child, as she shrugged off her own frailties. My parents, meanwhile, still come out with it on occasion. As for myself, I understand it but rarely use it. In other words, my family is an example of how an expression entered the language, took hold in a generation and then gradually slipped away, how English is constantly evolving and sifting words in an ongoing process of selection. We can treasure "San Fairy Ann" for all it represents in terms of personal and social histories, but also relish the continuing shared creativity which leads us towards new expressions on a daily basis.
"Inventing Truth", my Happenstance pamphlet, features the following poem:
San Fairy Ann
Wit amid blood and Belgian mud,
Nan invoked you daily. Your time
on our tongues and in dictionaries
might be running out, but I've passed
your syllables on to my son
in return for his slang from school.