Joke theft is the act of performing and taking credit for comic material written or performed by another person without their consent and without acknowledging the other person's authorship. This may be a form of plagiarism and can, in some cases, be copyright infringement. A comic who is known to steal jokes may be labelled with the epithet "hack" by other comics. A "hack comic" uses material that is unoriginal or which is blatantly copied from its original author.
Some cases of alleged joke theft are ambiguous, due to the possibility of simultaneous and coincidental discovery. Some comics have defended their re-use of other people's jokes as satire or as a calque (word-for-word translation). Other comics have claimed that their re-use was a type of "borrowing," or taking inspiration.
History
Vaudeville years
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.
1970s
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.
Several comics accused Robin Williams of stealing their material. David Brenner claimed that he confronted Williams personally and threatened him with bodily harm if he heard Williams utter another one of his jokes.
1990s
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 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.
George Lopez has accused Carlos Mencia ("Menstealya") 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.