I’ve just learned that “Nixon in China” contains the word “motherfucker.” What other operas, if written today, would include cursing?
My vote goes for “Tosca.” Certainly Scarpia has reason to yell “cocksucker” at Tosca after she fatally stabs him.
Jesus Christ Superstar already contains mild profanity. Judas sings “Just don’t say I’m damned for all time…”
Also, if Hair counts as opera, there’s a song called, I think, “Sodomy and Masturbation”.
“Sodomy, fellatio, cunnilingus, paederasty -
Father, why do these words sound so nasty?
Masturbation can be fun
Join the Holy orgy Kama Sutra, Everyone!!”
I wouldn’t consider Hair an opera, myself, but I love that song.
John Adams’ ‘The Death of Klinghoffer’ has the word ‘shit’ in Klinghoffer’s aria.
Alban Berg’s ‘Wozzeck’ has the puzzling euphemism ‘coughing’ for ‘pissing’ in Act I, sc. 4. In the original play, the Doctor is furious with Wozzeck because Wozzeck just pissed in the street, so he has no piss left to give the Doctor for a urine sample. Berg knew he was going to have enough trouble getting his opera onstage without having that vulgarity in it, so he changed the word for coughing. Most productions now use ‘piss’, though I did hear of one where they kept ‘cough’ and had the Doctor, clearly uncomfortable with the word ‘piss’, demonstrate through uncomfortable gesturing the word he was clearly too haughty to say.
I seem to remember the character of Aristotle Onassis swore in ‘Jackie O.’, but the opera was so unforgivably banal, I’ve thankfully forgotten the exact context. Please don’t make me try to remember it…
A bit more about Hair, The American Tribal Love-Rock Musical:
One of the songs, “Abie Baby”, has the lines “emanci-mother-fuckin-pator of the slaves” and “Shit, I’m not dying for no white man.”
In opera, how about Monterone cursing Rigoletto … 
George Enescu’s Oedipe would certainly contain the word “motherfucker” if written today.
Songs like “What the fck? What the fck? What the fcking fcking f*ck?” and lines like “Dip me in chocolate and throw me to the lesbians” all contribute to the general flavour.
No, Hair isn’t an opera, but this story is too good not to tell:
Some years back, I saw in the newspaper that an Oklahoma City magnet school–high school, not college–was performing Hair. This I had to see! (I kept flashing back (Oh, yeeeah, man-- Uh, where was I?) I kept flashing back to the Playboy cartoon, ca. 1969, where the principal is admonishing the teacher, “I don’t care what the vote was, the senior class play will not be Hair.” So my friend and I went to see it. It was heavily sanitized, of course, with the cuts in the expected places.
On the way out, I mentioned that I wished they’d distributed programs, and my friend said she had seen people with them, so I went back into the auditorium to try to find one abandoned under the seats. Which I did.
Up one the stage, a wussy-looking little teacher was taking video of the cast. Seemingly impromptu, the kids all burst into “Masturbation / Can be fun…”
The teacher stomped and waved his arms and fluted “Don’t ruin it! Don’t ruin it!”
Best moment of the whole evening for me!
I recall attending a performance of Carmen during which the entire audience gasped in shock when the supertitles revealed that Don Jose calls Carmen a bitch.