Played straight, then lampshaded into Cluster F-Bomb territory in Louis-José Houde's special Suivre la parade during an extended bit about his ex-girlfriend's abortion. He describes going home after the procedure and (after wishing his own father a happy birthday) listening to a new voicemail message from his agent: he's just won an award from a kids' TV station for "the performer that you'd would most like as a dad."
Houde:(after a long pause, quietly) ...Tabarnac. (audience laughs) I'm sorry, there's one swear word in the show, there it is — tabarnac. It's a tabarnac case, I have to, I'm sorry. At that moment in your life, I swear, that's what comes out — tabarnac. Tabarnac, tabarnac, tabarnac.
Context for English speakers: Tabarnac is a very offensive swear word in Quebec French.
Bill Cosby, famous for working clean, drops one in Himself:
Bill Cosby: So I asked, "What is it about cocaine that makes it so wonderful?" He said, "Well, it intensifies your personality." I said, "Yes, but what if you're an asshole?"
It's secondhand, but: Eddie Murphy did a hilarious bit about Cosby chiding him for his use of foul language. It culminates with Murphy-imitating-Cosby saying "Yooooooooooou (beat) cannot say (beat) FUCK. (beat) In front of people." In the mid-1980s, the mere suggestion that Bill Cosby actually said "fuck" is enough to bring the house down.
"Now, this doesn't happen to me very often, but about three weeks ago, I met a girl and she was real nice and she invited me to her apartment. So I went over there, and she had the best pussy I have ever seen —" [Audience laughter, cheers and catcalls] "Oh, now come on! I'm talkin' about her cat! Now that makes me sick, right there! No! No, you can't say anything anymore that people don't take it dirty, and I'm sorry, that disgusts me!" [Pause] "That cat was the best fuck I ever had, too."
Not sure if this qualifies as "stand up" but as there is no category for Sketch Comedy Record Albums... Monty Python's The Album of the Soundtrack of the Trailer of the Film of Monty Python and the Holy Grail has this in its "Introduction To The Executive Album Edition":
"Everything on this record has been designed to meet the exacting standards which you have naturally come to expect....There is little or no offensive material, apart from four cunts, one clitoris, and a foreskin. And, as they only occur in this opening introduction, you're past them now."
Steven Wright's act is generally devoid of any and all cursing. Given his tendencies towards literalism, though, it shouldn't come as any surprise that the one time his stage persona swore it was because he thought he was speaking French.
George Carlin is the champion of dirty words.
Used by Ron White in his act when discussing how he got kicked out of the debate team
Ron: I got kicked off the high school debate team for saying, "Yeah? Well, fuck you!". The other guy was speechless. I thought I had won!
British comedian Frank Skinner experimented with this trope while on tour, first by removing all swearing from his act and then by reintroducing only the most significant swearwords. He later started promoting the buzzword Intelligent Swearing.
Ray Romano, long known for being the wishy-washy husband on Everybody Loves Raymond, performed stand-up comedy at Carnegie Hall. He began as follows.
"Excuse me for a moment, ladies and gentlemen...Carnegie F<bleep>ing Hall. <wild applause> The only profanity of the night."
As part of an HBO special shortly after the last episode of Everybody Loves Raymond, he said "You have no idea how many times on that show I just wanted to shout 'Shut the fuck up, Debra! Shut the fuck up!'" He went on to say "This is Cable, I'm allowed to swear."
Billy Connolly is known for his barrage of F-words (and in his most recent material, the C-word) but earlier in his career he tended to avoid stronger swear words, replacing them with childish ones ("Jobby" instead of "Shit" for instance). As his career progressed, he gradually started using stronger language, leading to a wonderful Precision F Strike in a story about a Cardinal visiting a Roman Catholic school in Glasgow, Scotland. After a child tells the Cardinal to "fuck off", the offended holyman goes on a long tirade about how he studied hard to be in the position he was in today, ascending the ranks of the clergy to eventually sitting on the jury who elected Pope John Paul II. The punchline:
"....and you're telling ME to fuck off? YOU fuck off!!"
David Mitchell could strike you as a rather shy, calm and introverted person, and even when making one of his long and rather angry rants he usually watches his language. If he does swear, it's really a remarkable moment, such as an appearance on Adam Hills' The Last Leg, where he goes on a rant about tax avoidance including an ice cream analogy and no swearing at all, until the very end:
"So what we're doing is we're discouraging people from being nice and having a conscience... by taxing it. And that is the most fucking bonkers system that we could possibly have come across."