"I do have a cause, though. It is obscenity...
I'm for it." - Tom Lehrer
What is Lashon Hara?
(יג) מִֽי־הָ֭אִישׁ הֶחָפֵ֣ץ חַיִּ֑ים אֹהֵ֥ב יָ֝מִ֗ים לִרְא֥וֹת טֽוֹב׃ (יד) נְצֹ֣ר לְשׁוֹנְךָ֣ מֵרָ֑ע וּ֝שְׂפָתֶ֗יךָ מִדַּבֵּ֥ר מִרְמָֽה׃
א"ר ירמיה בר אבא: ארבע כיתות אין מקבלות פני שכינה: כת ליצים וכת חניפים וכת שקרים וכת מספרי לשון הרע.
כת ליצים דכתיב (הושע ז, ה) משך ידו את לוצצים כת חניפים דכתיב (איוב יג, טז) כי לא לפניו חנף יבא כת שקרים דכתי' (תהלים קא, ז) דובר שקרים לא יכון לנגד עיני כת מספרי לשון הרע דכתיב (תהלים ה, ה) כי לא אל חפץ רשע אתה לא יגורך רע צדיק אתה ה' לא יגור במגורך רע
Rabbi Yirmeya bar Abba says: Four classes of people will not greet the Divine Presence: The class of cynics, and the class of flatterers, and the class of liars, and the class of slanderers. The proof for this statement is as follows: The class of cynics, as it is written: “He draws His hand from cynics” (Hosea 7:5), i.e., God does not want to be in their presence; the class of flatterers, as it is written: “That a flatterer cannot come before Him” (Job 13:16); the class of liars, as it is written: “He who speaks falsehood shall not dwell before My eyes” (Psalms 101:7). The class of slanderers will not greet the Divine Presence, as it is written: “For You are not a god who has pleasure in wickedness, evil shall not sojourn with You” (Psalms 5:5), which means: You, the Lord, are righteous and evil shall not dwell with You in Your dwelling place. “Evil” here is referring to slanderers, as is evident from the continuation of the chapter, which states: “For there is no sincerity in their mouth; their inward part is a yawning gulf, their throat is an open tomb, they make smooth their tongue” (Psalms 5:10).
Dena Weiss, "In Praise of Privacy"
Privacy is about respecting the right of another person to control what is or is not seen, heard, or known about them. Lashon hara is designed to do just the opposite.
[...]
There is something inherently problematic in speaking about another person, even if you are saying something positive and trying to promote the person you are speaking about. Trying to enhance someone else’s reputation also creates expectations for their behavior, it also has the impact of controlling who that person is by determining how they might be perceived.
We're not going to look at this inside, but here's Maimonides approach, which codifies much of what we've seen implicit in other sections.
What is Nivul Peh?
בַּעֲוֹן נַבְלוּת פֶּה צָרוֹת רַבּוֹת, וּגְזֵירוֹת קָשׁוֹת מִתְחַדְּשׁוֹת, וּבַחוּרֵי שׂוֹנְאֵי יִשְׂרָאֵל מֵתִים, יְתוֹמִים וְאַלְמָנוֹת צוֹעֲקִין וְאֵינָן נַעֲנִין, שֶׁנֶּאֱמַר: ״עַל כֵּן עַל בַּחוּרָיו לֹא יִשְׂמַח ה׳ וְאֶת יְתוֹמָיו (וְאַלְמְנוֹתָיו) [וְאֶת אַלְמְנוֹתָיו] לֹא יְרַחֵם כִּי כֻלּוֹ חָנֵף וּמֵרַע וְכׇל פֶּה דּוֹבֵר נְבָלָה בְּכׇל זֹאת לֹא שָׁב אַפּוֹ וְעוֹד יָדוֹ נְטוּיָה״. מַאי ״וְעוֹד יָדוֹ נְטוּיָה״ — אָמַר רַבִּי חָנָן בַּר רָבָא: הַכֹּל יוֹדְעִין כַּלָּה לָמָּה נִכְנְסָה לַחוּפָּה. אֶלָּא כׇּל הַמְנַבֵּל פִּיו אֲפִילּוּ חוֹתְמִין עָלָיו גְּזַר דִּין שֶׁל שִׁבְעִים שָׁנָה לְטוֹבָה — הוֹפְכִין עָלָיו לְרָעָה. אָמַר רַבָּה בַּר שֵׁילָא אָמַר רַב חִסְדָּא: כׇּל הַמְנַבֵּל אֶת פִּיו — מַעֲמִיקִין לוֹ גֵּיהִנָּם, שֶׁנֶּאֱמַר: ״שׁוּחָה עֲמוּקָּה פִּי זָרוֹת״. רַב נַחְמָן בַּר יִצְחָק אָמַר: אַף שׁוֹמֵעַ וְשׁוֹתֵק, שֶׁנֶּאֱמַר: ״זְעוּם ה׳ יִפּוֹל שָׁם״.
Due to the sin of vulgar speech, troubles abound, and harsh decrees are renewed, and the youth among the enemies of Israel, a euphemistic reference to Israel, die, and orphans and widows cry out for help and are not answered, as it is stated: “Therefore the Lord shall have no joy in their young men, neither shall He have compassion on their fatherless and widows; for everyone is ungodly and an evildoer, and every mouth speaks wantonness. For all this His anger is not turned away, but His hand is stretched out still” (Isaiah 9:16). The Gemara explains: What is the meaning of the phrase: But His hand is stretched out still? Rabbi Ḥanan bar Rava said: Everybody knows why the bride enters the wedding canopy. There is no secret revealed. Nevertheless, anyone who speaks vulgarly about it, even if they, on High, sealed for him a decree of seventy years of good fortune, they will reverse it to bad fortune because of this sin. And Rabba bar Sheila said that Rav Ḥisda said: Anyone who speaks vulgarly, they deepen Gehenna for him, as it is stated: “The mouth that speaks perversity is a deep pit: he that is abhorred of the Lord shall fall therein” (Proverbs 22:14), i.e., Gehenna is deepened for one who speaks vulgarly. Rav Naḥman bar Yitzḥak said: Even one who hears vulgar speech and is silent is punished, as it is stated: “He that is abhorred of the Lord shall fall therein,” even if he himself does not speak at all.
It is, let us say, useful to notice that this not halakhic language. This is the language that rabbis use when they don't like something but have no halakhic hook on which to hang that objection.
It's also interesting to notice what constitutes vulgarity for them - speaking vulgarly about things that should be treated respectfully. It is not the topic itself, but the denigration of it that upsets them.
A Collection of Rabbinic Exclamations and Where They Can Be Found.
The words themselves are underlined in the sources with context.
״הָאֱלֹהִים!״ - ברכות כ״ד ב
God!
״ווי לדין״ - עבודה זרה י״א
Woe unto them
״חריא דעיזי״ - תענית ט׳
Goat dung
״חָרֵי חַמִּימֵי בְּדִיקּוּלָא בַּזְיָיא לְפוּמַּיְיכוּ״ - פסחים ק״י א
Hot feces in date baskets in your mouth
״בְּרִית!״ - פסחים ל״ח
The covenant!
״מָרֵיהּ דְּאַבְרָהָם!״ - שבת כ״ב א
Master of Abraham!
אָמַר רַב הוּנָא אָמַר רַבִּי יוֹחָנָן: הָיָה מְהַלֵּךְ בִּמְבוֹאוֹת הַמְטוּנָּפוֹת — מַנִּיחַ יָדוֹ עַל פִּיו וְקוֹרֵא קְרִיאַת שְׁמַע. אֲמַר לֵיהּ רַב חִסְדָּא: הָאֱלֹהִים! אִם אַמְרָהּ לִי רַבִּי יוֹחָנָן בְּפוּמֵּיהּ — לָא צָיֵיתְנָא לֵיהּ.
Rav Huna said that Rabbi Yoḥanan said: One who was walking in alleyways filthy with human excrement and he must recite Shema, he places his hand over his mouth and recites Shema. Rav Ḥisda said to him: By God! Even if Rabbi Yoḥanan had said it to me directly, with his own mouth, I would not have obeyed him.
ומסיימין בה הכי ווי לדין כד יקום דין
And they conclude in this fashion: Woe unto this one, Esau, when that one, Jacob, will arise, as this will cause Esau’s downfall.
אמר רב יהודה נהילא מקמי מיטרא אתי מיטרא בתר מיטרא פסיק מיטרא מקמי מיטרא אתי מיטרא וסימניך מהולתא דבתר מיטרא פסיק מיטרא וסימניך חריא דעיזי:
Rav Yehuda said that there is another sign of imminent rain: Drizzle before rain means that rain is coming. However, drizzle that falls after rain is a sign that the rain is stopping. Rav Yehuda provides an analogy by way of explanation: Drizzle before rain means that rain is coming, and your mnemonic is a sieve: Just as small quantities of flour drop from the sieve even before one begins to actively sift it, so too drizzle falls before rain. Conversely, drizzle that falls after rain signifies that the rain is stopping, and your mnemonic is goat dung. A goat’s initial droppings are large, whereas its latter droppings are small.
אָמַר אַמֵּימָר אֲמַרָה לִי רֵישָׁתִינְהִי דְּנָשִׁים כַּשְׁפָנִיּוֹת הַאי מַאן דְּפָגַע בְּהוּ בְּנָשִׁים כַּשְׁפָנִיּוֹת נֵימָא הָכִי חָרֵי חַמִּימֵי בְּדִיקּוּלָא בַּזְיָיא לְפוּמַּיְיכוּ נְשֵׁי דְּחָרָשַׁיָּיא קָרַח קָרְחַיְיכִי פָּרַח פָּרְחַיְיכִי
Ameimar said: The chief of witches said to me: One who encounters witches should say this incantation: Hot feces in torn date baskets in your mouth, witches; may your hairs fall out because you use them for witchcraft; your crumbs, which you use for witchcraft, should scatter in the wind;
כְּשֶׁבָּאתִי וְהִרְצֵיתִי דְּבָרִים לִפְנֵי רַבִּי אֱלִיעֶזֶר, אָמַר לִי: בְּרִית! הֵן הֵן הַדְּבָרִים שֶׁנֶּאֶמְרוּ לוֹ לְמֹשֶׁה בְּסִינַי. אִיכָּא דְּאָמְרִי: בְּרִית, הֵן הֵן הַדְּבָרִים שֶׁנֶּאֶמְרוּ לוֹ לְמֹשֶׁה בְּסִינַי? וְלָא טַעְמָא בָּעֲיָא?!
When I returned and recited these matters to Rabbi Eliezer, he said to me in excitement: By the covenant, these are the very matters that were stated to Moses on Mount Sinai. Rabbi Eliezer swore that this halakha had been transmitted over the generations going back to Moses on Mount Sinai. Some say he spoke in astonishment: By the covenant! Are these in fact the matters that were stated to Moses on Mount Sinai? And doesn’t this halakha require a reason? Since there is no explicit tradition in this regard, it is necessary to provide a reason for this distinction.
One of the hardest questions to answer about the Talmud is what register it speaks in.
By register, I mean the continuum from excrement -> poop - > crap -> $#!t, any of which would be a reasonable translation for חריא. The Romans were fascinated by the question of how vulgar any given insult was; while the rabbis of the Talmud mostly are not interested in that conversation. So it's hard to answer how they would have reacted.