In music halls and vaudeville, it was common for performers to "borrow" material. According to Milton Berle, etiquette only required that "the borrower add to the joke and make it his own". At the time there were few chances that a performer from one area would meet one from another and a single twenty-minute set could sustain a comic for a decade. Most jokes at the time were one-liners and there was little in the way of proof of a joke's origin, but the value of each joke was immeasurable to a comedian. Berle and Bob Hope had a long-standing feud due to Hope's accusation that Milton Berle had stolen some of his jokes. Berle never disputed the claim, but instead embraced the title "The Thief of Bad Gag".
Even the most famous of comics have found themselves, knowingly or unknowingly, stealing material. Bill Cosby admitted to stealing a joke by George Carlin involving an uneducated football player doing a television commercial. Cosby said that what makes the routine his own is the surreal phrase "little tiny hairs". Many years later, Carlos Mencia performed a bit about athletes and their parents that hearkened back to a Cosby bit from his album, Bill Cosby: Himself.
In the 1970s, joke theft became more prominent with the boom in popularity of comedy. The 1980s and 1990s saw the popularity of stand-up comedy continue to increase. The advent of pay-cable networks afforded comics the opportunity to perform their routines unfettered. With this came a new type of joke theft in which the first comic to tell a stolen joke on some sort of media became the one associated with the joke.
Robin Williams was accused of stealing material from another comic. David Brenner claims that he confronted Williams personally and threatened him with bodily harm if he heard Williams utter another one of his jokes.
For many years, Denis Leary had been friends with fellow comedian Bill Hicks. However, when Hicks heard Leary's 1993 album No Cure For Cancer, he felt Leary had stolen his act and material, and the friendship ended abruptly as a result. At least three stand-up comedians have gone on the record stating they believe Leary stole not just some of Hicks' material but his persona and attitude. As a result of this, it is claimed that after Hicks' death from pancreatic cancer, an industry joke began to circulate about Leary's transformation and subsequent success (roughly; "Question: Why is Denis Leary a star while Bill Hicks is unknown? Answer: Because there's no cure for cancer").
In a 2008 appearance on The Opie and Anthony Show, comedian Louis C.K. claimed that Leary stole his "I'm an asshole" routine, which was then expanded upon and turned into a hit song by Leary. On a later episode of the same show, Leary challenged this assertion by claiming that he (Leary) co-wrote the song with Chris Phillips.
In his memoir Gasping for Airtime, Jay Mohr admitted that he lifted an entire routine from Rick Shapiro's act for a 1995 Saturday Night Live sketch. He stated that Shapiro sued the show and was financially compensated, but Shapiro later disputed that he received any compensation.
2000s and 2010s
Louis C.K. has maintained a relatively quiet rivalry with Dane Cook over three bits on Cook's album, Retaliation, that allegedly bear some resemblance to three bits on C.K.'s album Live in Houston. C.K. and Cook portray this rivalry with comedy and sincerity in an episode of C.K.'s series Louie.
Joe Rogan has been vocal about fellow comedian Carlos Mencia's alleged joke thievery. In a 2005 blog post entitled "Carlos Mencia is a Weak Minded Joke Thief", Rogan denounces Mencia as a "phony" and encourages his fans to "stop supporting joke thieves."
George Lopez has also accused Mencia of plagiarizing his material and claimed that the two once had a physical altercation over the alleged plagiarism. However, fellow comedian Ted Sarnowski countered this claim and stated that it was he, not Lopez, who had originally penned the joke and that he had given Mencia permission to use it when he discovered that Lopez had stolen it.
The Comedy Central show, South Park made light of the Mencia controversy in an episode titled "Fishsticks" when Eric Cartman and Mencia take credit for a hilarious joke written by South Park Elementary School student Jimmy.
In 2010, Mencia appeared on two episodes of WTF with Marc Maron. In the first episode, Mencia denied stealing any material, and stated his being blacklisted was a result of not responding to the allegations quickly or effectively. In the second episode, Maron first interviews comedy writers who worked for Mencia and allege that Mencia stole stand-up material from them. When confronted, Mencia said he was allowed to because he was paying them. One comic speaks of Mencia encouraging him not to pursue stand-up in Los Angeles, but learned this was a manipulation so Mencia could use his jokes without him knowing. Maron then confronts Mencia with these allegations, which he denied.
In 2010, Italian comic and satirist Daniele Luttazzi was accused by anonymous bloggers of having plagiarised many jokes from comedians such as George Carlin, Mitch Hedberg, Eddie Izzard, Chris Rock, Bill Hicks and Robert Schimmel. However, in a personal blog entry published five years prior, Luttazzi himself offered his blog readers a prize if they were able to identify a "nugget" (i.e. a reference to a famous joke), calling the game a "treasure hunt". He says he adds references to famous comedians' jokes to his work as a defense against the million-euro lawsuits he has to face because of his satire. (In March 2012, Luttazzi won a legal battle against La7 broadcasting company, which in 2007 abruptly closed his late show "Decameron", accusing him, among other charges, of plagiarism from Bill Hicks. Sentence: It was original satire, not plagiarism. Luttazzi got 1 million 2 hundred thousand euros as compensation.)  He calls this ruse "the Lenny Bruce trick" (named for the comic of same name). Luttazzi asserts that the jokes he references are not "plagiarized" but "calqued", which is a fair use of original material. In 2014, an academic paper explained why Luttazzi's jokes are his own and not "plagiarised" ones. 
In 2011, Australia's Got Talent contestant Jordan Paris presented an act of stand-up comedy and quickly proceeded to the semi-finals. However, it was later revealed that he had plagiarised his jokes from comedians Lee Mack and Geoff Keith. The television network gave him a chance to redeem himself and allowed him to compete in the semi-finals using his own material. Paris' effort this time was self-deprecating, joking about his plagiarism and his large teeth. The first joke went well, but the rest went downhill. It was later found out that the joke that went well – "I just sacked my two writers – Copy and Paste" – had been done in 2009 by comedian Jeffrey Ross, about Brad Garrett, at a roast of Joan Rivers. Ross had said, "This guy has two writers, their names are Cut and Paste."
In January 2012, blogger and comedian Troy Holm was ridiculed on the social networking site Facebook for stealing jokes and stories from comedian Doug Stanhope and posting them to his blog from 2010, claiming them as his own work, including Stanhope's "Fuck someone uglier than you" routine, which was found on Stanhope's Acid Bootleg. Troy Holm also plagiarized Stanhope's story of an encounter with a transsexual prostitute nearly verbatim, substituting himself as Stanhope, and changing a few small details, causing a backlash from Stanhope's fans. This catapulted Troy Holm into an internet icon which started the "Occupy Troy Holm" Movement. Stanhope commented on the Occupy Troy Holm Facebook page that "To the few people who seem to think this is overboard...and it is...I don't think that you know the levels to which this guy has been ripping me off. He didn't take a tit-fuck joke and use it as a status update. He's been living my entire life as though it was his, changing some names and then promoting with twitters... Look at his site and most the entirety of it is me, including the comments where he uses my stuff to pass as his own conversation. And on Twitter. So who is he ripping off for that stuff that isn't mine?"
In June 2012, a live show named Joke Thieves was launched in one of the longest-running comedy clubs in London, Downstairs at the King's Head (Crouch End). The show was also performed as part of the Free Festival at the Edinburgh Fringe in August 2013. The London launch night was reviewed by U.K. comedy website, chortle.co.uk, which called it "an undoubted hit" and "the birth of a new cult comedy night". Guest comedians are paired up on the show by the audience and perform their own material in part one before stealing each other's for part two. A pilot of the Joke Thieves show was developed by The Comedy Unit and recorded for BBC2 in August 2014 at BBC Scotland's studios in Glasgow, UK.
On 29 March 2015, Pete Davidson accused Natasha Leggero on Twitter of stealing one of the jokes he performed on the Comedy Central Roast of Justin Bieber. Leggero appeared with Davidson on the program. The joke in question was repeated on the Comedy Central program, @midnight.
Amy Schumer has also been accused of stealing material as recently as early 2017. Comedian Patrice O'Neal made jokes about different sex positions. In her recent special, Amy Schumer makes her closer with two jokes that were similar to Patrice's, the only difference being the name of the position. Schumer has had multiple instances of possible thievery, which she denies, and refers to as "parallel thinking". She has been accused of stealing jokes from Dave Attell, Marc Maron, John Mulaney, Wendy Liebman, Dave Chappelle and many others in her new special The Leather Special.
In other media
Joke theft is not limited to stand-up comedy. Often jokes in film and television shows are taken from comics or even other media. Dick Cavett wrote about joke theft in his autobiography. He'd written a bit about eating Chinese-German food and, an hour later, being hungry for power. After a few days of performing the bit, he discovered a column by Earl Wilson which attributed the joke to Rip Taylor. However, after calling Taylor to ask him to stop using the bit, he discovered that not only had Taylor never performed the bit, he had never even heard it and laughed heartily at the joke's humor. It was then that Cavett discovered that some journalists often falsely attribute jokes to the wrong comics.
Cavett and Woody Allen often cited to each other the many instances of their jokes appearing in television shows without their permission, sometimes even falsely attributed to each other. Allen's jokes, when he still lacked access to television, were regularly stolen by top mainstream shows The Red Skelton Show and Laugh In. This proved extremely painful to Allen.
Several episodes of The Simpsons, including "Missionary: Impossible", "Treehouse of Horror XIII" and "The Italian Bob" have poked fun at Family Guy, implying that MacFarlane's show is guilty of stealing jokes and premises from the Simpsons. However, the producers of both shows have said that there is no serious feud between the two of them and their shows.
In 2017 the Australian television show host Grant Denyer was interviewed on the radio programme The Grill Team, which is on 2MMM. In the interview, The Grill Team's co-host Matty Johns told an amusing anecdote about introducing a child to the board game Test Match. Later that morning, Grant Denyer was interviewed on the radio programme The Kyle and Jackie O Show, which is on KIIS 106.5. In that interview, he told the same anecdote about Test Match, passing it off as his own. 
Recourse and consequences
There is, historically, very little legal recourse taken in cases of joke theft. Some comics, however, have chosen to exact their own justice. W. C. Fields reportedly paid fifty dollars to have a thieving comic's legs broken.
"You have a better chance of stopping a serial killer than a serial thief in comedy," said comedian David Brenner. "If we could protect our jokes, I'd be a retired billionaire in Europe somewhere – and what I just said is original."
- Berle, Milton (1989) Private joke file, Introduction, p.xxiii quotation:
Of course, in the days of vaudeville, it wasn't uncommon for a performer to "borrow" a joke from another performer. Etiquette demanded only that the borrower add to the joke and make it his own. Bert Williams, a star of the Ziegfeld Follies, pilfered a story about fish and added enough laughs to turn it into a classic fifteen-minute routine. Naturally, that routine happens to be in my file.
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Woody's best lines would show up, while he was still confined to little Village clubs, on the Red Skelton show and that alleged entertainment, Laugh-In.
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The rivalry is very affectionate...
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You know, it's funny. Matt Groening and I actually have a great relationship...
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