Even in discussions about modesty, almost incredibly, one sees some people speak immodestly - i.e. with vulgar language, expletives and other illicit and sinful behavior. Why is this? Shouldn't we, as Traditional Catholics, know that such speech does not befit Christian lips, especially lips that have received the Lord in Holy Communion? Thoughts?

"ON THE VICE OF SPEAKING IMMODESTLY – St. Alphonsus
ON THE VICE OF SPEAKING IMMODESTLY.
“He touched his tongue, …. and the string of his tongue was loosed.” MARK vii. 33, 35.

IN this day’s gospel St. Mark relates tlie miracle which our Saviour wrought in healing the man that was dumb by barely touching his tongue. “He touched his tongue and the string of his tongue was loosed.” From the last words we may infer that the man was not entirely dumb, but that his tongue was not free, or that his articulation was not distinct.
Hence St. Mark tells us, that after the miracle he spoke right. Let us make the application to ourselves. The dumb man stood in need of a miracle to loose his tongue, and to take away the impediment under which he laboured. But how many are there on whom God would confer a great grace, if he bound their tongues, that they might cease to speak immodestly! This vice does great injury to others. Secondly, it does great injury to themselves. These shall be the two points of this sermon ...

9. Be attentive, then, my brethren, and guard your selves against speaking immodestly, more than you would against death. Listen to the advice of the Holy Ghost: ”Make a balance for thy words, and a just bridle for thy mouth; and take heed lest thou slip with thy tongue and thy fall be incurable unto death.” (Eccl. xxvhi. 29, 30.)
”Make a balance” you must weigh your words before you utter them and”a bridle for thy mouth” when immodest words come to the tongue, you must suppress them; otherwise, by uttering them, you shall inflict on your own soul, and on the souls of others, a mortal and incurable wound. God has given you the tongue, not to offend him, but to praise and bless him.
”But, ” says St. Paul, “fornication and all uncleanness, let it not so much as be named among you, as becometh saints.” (Ephes. v. 3.) Mark the words”all uncleanness. ” We must not only abstain from obscene language and from every word of double meaning spoken in jest, but also from every improper word unbecoming a saint that is, a Christian. It is necessary to remark, that words of double meaning sometimes do greater evil than open obscenity, because the art with which they are spoken makes a deeper impression on, the mind.
10. Reflect, says St. Augustine, that your mouths are the mouths of Christians, which Jesus Christ has so often entered in the holy communion. Hence, you ought to have a horror of uttering all unchaste words, which are a diabolical poison. ”See, brethren, if it be just that, from the mouths of Christians, which the body of Christ enters, an immodest song, like diabolical poison, should proceed.” (Serm. xv., de Temp.) St. Paul says, that the language of a Christian should be always seasoned with salt. ”Let your speech be always in grace, seasoned with salt. ”(Col. iv. 6.)

Our conversation should be seasoned with words calculated to excite others not to offend, but to love God. ”Happy the tongue,” says St. Bernard, ”that knows only how to speak of holy things!”

Happy the tongue that knows only how to speak of God! brethren, be careful not only to abstain from all obscene language, but to avoid, as you would a plague, those who speak immodestly. When you hear any one begin to utter obscene words, follow the advice of the Holy Ghost: ”Hedge in thy ears with thorns: hear not a wicked tongue.” (Eccl. xxviii. 28.)

“Hedge in thy ears with thorns” that is, reprove with zeal the man who speaks obscenely; at least turn away your face, and show that you hate such language. Let us not be ashamed to appear to be followers of Jesus Christ, unless we wish Jesus Christ to be ashamed to bring us with him into Paradise" http://www.traditionalcatholicpriest.com/2017/08/19/vice-speaking-immodestly-st-alphonsus/

Indeed, my biggest problem is with the GD term, or the use of Our Lord's name as a curse word, especially when somebody injects the F word between Jesus and Christ.

Rest are vulgar of course and low class, but not nearly approaching the severity of these two (above) and the other blasphemous ones.

Vulgarity is an interesting topic.  Many of our current dirtiest four-letter words were simply normal words in Anglo-Saxon.  But why is "copulate" an OK word to use but the F word is not?  After the Norman invasion, the Normans/French considered the Anglos to be barbaric, and their language, filled with mono-syllabic words, to be crude, sounding to their ear like grunts and groans.  Perhaps they were just efficient?  :) Why use 3 syllables to say something when you can say it in 1?

In any case, our Jєωιѕн overlords have deemed it OK to say GD phrase on radio or television but you can't say sh*t ... not without getting a fine.  So a crude way of saying poop is worse than blaspheming God?

Are they sinful?  Are they mortally so?  To be clear I'm asking about swearwords other than the Lord's Name in vain.

I once heard a priest say that swearing was a mortal sin but I wasn't given a clear source on why.

I'm not certain.  My general impression that it would not be, per se, but I imagine that could be exacerbated into grave sin by the context or the severity.  I did not make it to the moral theology classes at seminary, though, so I would ask a priest.  Father Kramer is floating around the forum, so perhaps he would be one to ask.

Let's assume for the sake of argument that there's no particularly just reason for using the language, but its also not meant to be sɛҳuąƖly explicit.  

Does Fr. Kramer go by that username or is he under a pseudonym?  

Don Paulo.

Don Paulo.

Don paolo

Quote If a priest said that swearing is a mortal sin, then I would stop swearing and confess my mortal sin. No big deal ...

"Kill them all, let God sort them out"

Yes, it is a mortal sin. Ugly vile words that are blasphemous are against the Second Commandment. Foul words that are impure are against the Sixth Commandment.  

I encourage everyone to read the whole sermon of St. Alphonsus posted in the OP. I only quoted the first and last portions for brevity's sake. St. Alphonsus gives clear authorities from Scripture and clear reasons why swearing is as such a mortal sin that, if not repented of, will lead to hell.

Mark in para 9 the words, "when immodest words come to the tongue, you must suppress them; otherwise, by uttering them, you shall inflict on your own soul, and on the souls of others, a mortal and incurable wound."

In para 8, "God punished both of them: one became blind, and a sore broke out on the other, which produced deadly spasms. Henry Gragerman relates (in Magn. Spec., dist. 9, ex. 58), that one of those obscene talkers died suddenly and without repentance, and that he was afterwards seen in hell tearing his tongue in pieces; and when it was restored he began again to lacerate it."

In para 7, "O God! how great, were it in their power to weep, would be the wailing of the angel-guardians of these poor children that are scandalized and brought to hell by the language of obscene tongues!"

In para 6, "Besides, by using immodest language, you expose yourself to the proximate danger of falling into unchaste actions: for, according to St. Jerome, as we have already said, ”he who delights in words is not far from the act." etc etc etc.

Besides, those who swear frequently will find themselves falling into all kinds of other vices they will struggle to remove, unless they remove the bad practice of using indecent words at its root. When they come to mind, as St. Alphonsus says in para 9, suppress them. St. Alphonsus also cites St. Paul in Sacred Scripture there, "”But, ” says St. Paul, “fornication and all uncleanness, let it not so much as be named among you, as becometh saints.” (Ephes. v. 3.) Mark the words”all uncleanness."

And while it is an admirable sentiment that you would stop swearing if a Priest told you to, do be a little careful on the "no big deal" part. The early Church, as St. Louis Montfort witnesses, used to stipulate 7 to 10 to 15 years of penance for each single mortal sin:

"Now these Canons exacted seven and sometimes ten or fifteen years' penance for one single mortal sin, so that a person who was guilty of twenty mortal sins would probably have had to perform a seven year penance at least twenty times, and so on." http://www.catholictradition.org/Classics/secret-rosary49.htm

Much much easier and better for all of us to entirely avoid the habit altogether, I think, than, having gotten into it, to hope not to have to make much painful reparation for it later on, either in this life, or what may perhaps be even more long and rigorous, in Purgatory.

God Bless.