One of the better known examples was when Tosh was doing stand-up and crossed the line when he made a rape joke. A female member of the audience heckled him for being offensive. Tosh then crossed the line a second time by asking how funny it would be if that girl got raped right now.
That and slowly whittling his jokes down to where only three or four people get it.
While he certainly qualifies, Tosh claims that within his circle of friends, his sense of humor is actually the more mild/mainstream. Take from that what you will.
Lisa Lampanelli's racist humor crosses every possible line in every possible way.
Jimmy Carr has based his entire stand-up career on crossing the line twice, thrice, quarce, whilst using as many rude words as possible. Needless to say, you either love love him or hate him. A radio host once asked him if there are any lines he's unwilling to cross. Jimmy said he leaves that up to the audience: if he tries out a new joke and nobody laughs, then evidently that one is going too far. If the audience does laugh, however, then obviously the joke must be funny, so he'll keep using it.
"I don't know where the line is until I've crossed it!"
Diane Spencer (not that one) appears to be making a career of this. One standout is her fantasy about sleeping with Prince Harry (to perpetuate the ginger race), in spite of, well...
Say my name, Harry. C'mon, say all of it!—All right, all right, don't cry, please don't cry.
George Carlin, who once said "I think it's the duty of the comedian to find out where the line is drawn and cross it deliberately."
"There's a line in the sand, right, and you can't even see the line in the sand. You are actually out of sand, into, like, into tropical tundra regions."note For context, Boyle had just made a suggestion that British television broadcast anti-speeding PSAs featuring "footage of Richard Hammondtrying to remember his own wedding day."
All of "Best Disease Ever" from the title onward, concluding with hypothetical Alcoholics Anonymous member Richie K in Norm's cheerful deadpan.
One time I was under the influence of the demon rum, and I started punching my newborn in the face. I kinda looked down on my fist and it was all bloody with, uh, I don't know what it was. It was either from my knuckles or my son's skull.
Riffing on a news story about a woman who had disappeared, he spends some time lampooning a number of tropes associated with missing persons. He then goes on to give an extremely detailed description of how he would kidnap and murder a woman if he were so inclined. At one point, he described the act as "doing that thing that makes me feel like God..."
Richard Pryor, made especially funny by the fact many of the things he describes actually happened to him.
I'M GILBERT GOTTFRIED, AND I'M GOING TO KILL YOU MOTHERFUCKERS FOR NOT MENTIONING ME! AND THEN I'M GOING TO RAPE A BITCH OR TWO!
This is pretty much Gottfried's whole act. He once famously joked about 9/11 only three weeks after the event at the Friar's Club roast of Hugh Hefner. The audience booed Gottfried, feeling it was much too soon for such jokes. How did he defuse the situation? By launching into a recital of The Aristocrats...it was hilarious. NASA scientists are still trying to calculate just how many times he crossed the line that night.
From about the same time as Andy Kaufman, we have Michael O'Donoghue, who was an editor for the National Lampoon and its radio show, head writer for Saturday Night Live when it first started, and co-writer of Scrooged. This is the man who had an office full of nude amputee pin ups, spray painted the word "DANGER" on the NBC studio wall after asking what the show lacked, and almost got a skit to air portraying the head of NBC as Hitler in the bunker. Needless to say, they fired him over his outrageous attempt to create his own show that spoofed Mondo movies.
Bill Maher, of course, especially in Real Time with Bill Maher. Although applying this to political jokes is what gets him in the most trouble, he arguably goes even further outside political jokes.
Doug Stanhope, arguably more than anyone else on this list.
Don Rickles whose act mostly consists of berating his audience, usually using every cultural, racial, and religious stereotype he can cram in.
Gabriel Iglesias doesn't usually pass too far over the line, but there's one story that's been pulled from his Comedy Central stories and even nearly got him banned from The Tonight Show. The story begins with Gabriel and a friend passing through a town and learning an old comedy buddy of theirs is performing. Gabriel wants to prank call the buddy, tell them they have a gift basket for him, and describe it as being filled with all sorts of items that black people are stereotypically known to like. Then Gabriel & his friend realize they have a couple of hours to kill and proceed to actually make the basket...
And then asking for help assembling said racist gift basket from staff at the store, as well as the black woman at the reception desk at the hotel. The staff were, according to the story, delighted about the idea, and very helpful; while the receptionist was decidedly less so... until they offered her a hefty tip to deliver said basket.
Anthony Jeselnik regularly crosses as many lines as possible in his standup comedy. In 2013 he did a sketch called "Shark Party", making light of a man who had recently been killed in a shark attack in New Zealand. The episode was banned from being rerun, and Jeselnik received death threats online from offended New Zealanders.
The late Robert Schimmel's act basically opened up the door to his (and everyone else's) bedroom. And it was hilarious.
He never knew when to stop: Arabic poet Abu Nuwas. Folk tales made him jester of Harun al-Rashid and gave us the following jewel. He once hid behind a curtain and pinched Harun in the backside. Harun was royally miffed and sentenced him to death. But he was a good ruler and gave Nuwas the opportunity to defend his action. "I'm so sorry, Lord! I thought it was your wife!" Harun had to laugh so hard that he pardoned him.
Jeff Dunham. This is pretty much the point of Achmed the Dead Terrorist.
Stephen Lynch. Many of his songs rely on shock humor and deliberate crossing of many taboos, particularly laughing at the disabled and the mentally challenged. The way he does it, though...
Ross Noble's reliance on improvised comedy and following bizarre tangents can sometimes lead to this, such as during one of the shows on his Unrealtime DVD when a joke which begins with the audience smearing cold mud on themselves to hide from The Predator ends with him discussing the mating call of a herd of retarded Jesuses. Ross himself acknowledges this:
Ross: If that was the line there, then up until now I've just been... (leans over the imaginary line) ...and now I've just gone "Woohoo!" (runs to the other side of the line waving his arms in the air)
British comedian Alan Carr rarely did this type of joke, but a notable one was this:
I just attract bad luck. How many people do you know who've been sexually assaulted on a Jack the Ripper-walk? I thought it was part of the experience!
Lewis Black, which is an absolute given seeing as how he's an angry foul-mouthed comedian.
It's widely thought that Michael Richards' 2006 Laugh Factory meltdown towards some Black hecklers was an attempt at this that badly backfired due to losing track of which side of the line he was standing on.
immediately after it happened, which ended up costing him his job at Aflac.