Here’s a fun passage in Dashiell Hammett’s ‘The Gutting of Couffignal’, a great story that opens The Big Knockover and Other Stories (whose colourful crooks’ names I listed recently). Skip the first paragraph if you want to avoid spoilers.
‘There’s your choice, Flippo,’ I summed up for him. ‘All I can give you is freedom from San Quentin. The princess can give you a fat cut of the profits in a busted caper, with a good chance to get yourself hanged.’
The girl, remembering her advantage over me, went at him hot and heavy in Italian, a language in which I know only four words. Two are them are profane and the other two obscene. I said all four.
Profanity is when something is considered insulting to a religion, its god(s), or people’s beliefs in them. Obscenity involves offense to taste or common decency, something vulgar enough to be taboo in a given context (often relating to sex or bodily functions). There are legal nuances to both terms, but I won’t get into that here.
Two profane and two obscene words, all presumably common swears, or common in the early 20th century. I can guess what they might be, but maybe Hammett didn’t have four particular words in mind. There are Italian speakers in my family; I’ll run it by them. For research.
Sentence first 
I suppose I’m “incorrect,” but I don’t use obscene to refer to things that are taboo (usually sexual) – or not only that way. I use it to refer to things that I find to be extreme in their self-centeredness in total disregard of their impact on other people. Such as use of the environment in ways that harm many others (e.g. gross energy consumption by many people from my country), or conspicuous consumption.
I suppose my use of “obscene” for that kind of action, rather than for sexual things, is a way to throw people somewhat off base by a non-standard use of the word, and perhaps get them to notice that something is wrong with excessive consumption. Me, self-righteous and judgmental??? Never!
Oh, and I don’t know any Italian, so I can’t help on that!
I am Italian and I suspect the two profane Italian words might be one single blasphemous expression, bestemmia in Italian. I’ve just found out that bestemmie can be divided into several categories: “heretical” (against faith),”simple” (a mere insult), “imperative” (wishing ill against God) and also “immediate” (directly against God) and “mediate” (against the Virgin, one or more saints, or anything sacred).
I‘ve seen bestemmie in print mainly in English-language novels, either set in Italy or involving Italian characters (I still remember the first time I came across one, in Captain Corelli’s Mandolin!). Most Italians find bestemmie disturbing – they are on a high “taboo level” and hardly found in mainstream writing – but I doubt .non-native authors are fully aware of their impact.
Joy: That’s not incorrect at all; it’s another (fully standard) sense of obscene. I use it too, sometimes in ways similar to those you mention, but I left it out of this discussion because I was focusing on the language-related sense of the word. Thanks for bringing it up, though.
Licia: Thank you for the helpful categorisation of blasphemy in Italy. I’m ignorant of the connotations and relative offensiveness of the few Italian swear terms I know (which in any case are more rude or obscene than profane), so I’m grateful for the insights.
Hispanophones are big on insults that are both profane and obscene. Wikipedia mentions Me cago en Dios / la Virgen / la hostia / el copón ‘I shit on God / the Virgin / the communion wafer / the ciborium’ as typical.
Here’s anIrish curse generator from the excellent Sabhal Mòr Ostaig web site. Pick English phrases, click, and out comes “sweet poetry and melodious Irish” (Flann O’Brien) in the objurgatory mode. Sample: “Go gcreime paca Fomhórach ólta do chuid infheistíochta.”
The etymology of bestemmia is Greek blasphemia, not too surprisingly. More surprisingly, another descendant is Spanish lastimar ‘pain, hurt’, as in the common phrase ¡Qué lástima! ‘What a pity!’
Enlightening as always, John. I had fun wandering around the Sabhal Mòr Ostaig website, and after some experimentation with the curse generator I settled on Go ndubhaí na gráinneoga mioscaiseacha do thóin gan mhaith (“May the malevolent hedgehogs blight your worthless butt”).
Which reminds me: the Pogues originally called themselves Pogue Mahone, but they had to change the name when the BBC got complaints from the Hebrides.