Saint Fiacre was an Irish saint, to whom some in France are especially devoted. He died around 670AD.
Saint Fiacre is the patron saint of sexually transmitted diseases. Some say he achieved this honour because he was terrified of women. This can be a reasonably fool-proof way of avoiding such a disease (unless, as some like to say, one sits on a public toilet and contracts it from the seat).
However, the truth has emerged.
One day, a Frenchman called Etienne was having a night out with his Irish mate Sean. Sometime later Etienne discovered he had a sexually transmitted disease.
“Oh fiacre!” said Etienne. “I have contracted fiacre-in’ syphilis.”
“Fiacre! Surely not!” exclaimed Sean. “How the fiacre did that happen?”
“It must have been when we fiacred that prostitute,” said Etienne.
“Holy fiacre!” wailed the also-now-syphilis-riddled Sean.
Sean’s vocal ejaculation was overheard, and thus sprang up the cult of Saint Fiacre.