The F- word.
I hate it. I always tell the story of an Irish priest in Lourdes who warned me never to use that word because it is the devil's favorite - he never explained why it was his favorite, but he gave me a severe penance for using it.
Today it is almost common usage - even by people who wear lots of amulets and sacramentals to ward off the devil, even those who drench themselves in old-ritual-blessed holy water and sprinkle exorcism salt around their house and yard. Or - worry about tunnels in Switzerland. Yet they speak the devil's language.
I even hear little kids use it - really little kids, "Oh - that's so f-ing cool!" Where did they learn that sort of language? Many picked it up at home. Even moms and dads use the word and make allusions to what it means as they constantly converse on their phones, in front of their kids as they chauffeur them to and from their latest competitive activity.
Immodest dress, immodest speech - and one expects to be chaste and pure, or even Christian? You think?
"Filthy talk makes us feel comfortable with filthy action. But the one who knows how to control the tongue is prepared to resist the attacks of lust." - Saint Clement of Alexandria
“The man of impure speech is a person whose lips are but an opening and a supply pipe which hell uses to vomit its impurities upon the earth.” - Saint John Vianney
"What could be more out of keeping with our holy religion than impure language? It outrages God. It scandalizes our neighbor. Can a Christian really afford to occupy his mind with such horrible images; a Christian who has been sanctified by contact with the most adorable Body and Blood of Christ?" - Saint John Vianney
O men, how long will your hearts be closed, will you love what is futile and seek what is false? - Ps 4