Usually when people speak of swearing cursing or cussinng they mean using filthy words and speach.If your friend has this problem, here is a short article about the problem containing Bible quotes:
Vulgarity and Innuendo
"The final category under consideration is vulgarity and innuendo.Included in this category are: dirty jokes, sexual implications and undertones, filthy language referring to bodily functions or anatomy, and other inappropriate topics, which should not be publicly or lightly discussed. Whereas vulgar speech contains direct and explicit references, innuendo contains hints, winks, gestures, facial expressions, and other subtle forms of communication, which quietly express vulgar thoughts. It is this subtle vulgarity and crude speech that makes up the vast majority of “adult humor”, which often sails over the heads of innocent and naive children. It is this language that causes adults to wrinkle their mouths and snicker softly as another hints at explicit themes without actually articulating them. As before, we find that the Scriptures strongly condemn this type of language:
"Therefore be imitators of God as dear children. And walk in love, as Christ also has loved us and given Himself for us, an offering and a sacrifice to God for a sweet-smelling aroma. But fornication and all uncleanness or covetousness, let it not even be named among you, as is fitting for saints; neither filthiness, nor foolish talking, nor coarse jesting, which are not fitting, but rather giving of thanks. (Ephesians 5:1-4)
"But now you yourselves are to put off all these: anger, wrath, malice, blasphemy, filthy language out of your mouth. (Colossians 3:8)
“A Christian is to have his mind set on higher, nobler, spiritual things. Therefore such communication should not be appealing to him. Neither, should it be something upon which he dwells and is therefore even able to imagine, much less utter. Whether spoken directly, or implied through innuendo, the ideas actually communicated by this “filthy language” are the same and are therefore in error.”