(covers information from several alternate timelines)
A joke is "a witticism, a gag, [or] a bon mot, a fluctuation of words concluding with a trick ending." (TNG: "The Outrageous Okona") It can also be described as "a story with a humorous climax." (Star Trek IV: The Voyage Home) Or as "a verbal comment or gesture designed to provoke laughter." (VOY: "Drone")
In 2268, Ensign Pavel Chekov reported that the Enterprise would be only one parsec away from a Klingon outpost, "close enough to smell them". As Commander Spock explained that odours cannot travel through the vacuum of space, Chekov claimed it was "just a little joke". Spock replied, "Extremely little". Not long after this, Cyrano Jones was attempting to sell tribbles aboard Deep Space Station K-7. His asking price was ten credits and when the barman tried to bargain, eventually going to four credits, Jones asked "Is that an offer or a joke?" The barman replied that it was an offer and Jones countered "That's a joke." (TOS: "The Trouble with Tribbles")
When Wesley Crusher made a visit on the USS Enterprise-D in 2370, Data greeted him with a joke and said, "A cadet is on board, we should call the security." Data later tried to clarify that he intended to make a joke and meant no ill. (TNG: "Journey's End")
That same year, in the mirror universe, Doctor Julian Bashir met Odo's mirror counterpart, a cruel individual who ruled over the workers at the ore processing facility on Terok Nor with his Rules of Obedience. When Bashir told him that his designation was "Bashir, Julian," he slapped him and told him that his Rule of Obedience #14 was "no jokes." Later, when Bashir told him that he had been practicing medicine, he slapped him again and reminded him of Rule #14. (DS9: "Crossover")
During a mission to rescue a Federation informant on Dominion-occupied Soukara, Worf claimed to Jadzia Dax that he has a sense of humor, and was "considered to be quite amusing" when serving on the USS Enterprise-D, to which Dax responded that it "must have been one dull ship." Worf found that jab to be a joke, that he understood it, but did not find it funny. (DS9: "Change of Heart")
When Captain Kathryn Janeway and Seven of Nine were captured by Arturis, Seven claimed to not understand that in her role as captain, Janeway cannot always be friends with the crew serving under her, but that if they were to be assimilated, she would understand. She then clarified that she meant that as a joke, citing Janeway's encouragement that she develop a sense of humor. (VOY: "Hope and Fear")
While Vulcans are not unable to understand the concept of jokes, they find them unnecessary and difficult to comprehend. During their encounter with the Dream Aliens, the USS Voyager crew all suffered from nightmares. When B'Elanna Torres, Tom Paris, Harry Kim, and Neelix recounted theirs, they wondered what the nearby Vulcan Tuvok's dream was. Neelix suggested elements of a Vulcan nightmare might include being stranded on a planet in which the only form of communication is laughter. During most of Voyager's journey, Neelix made it his goal to make Tuvok laugh. (VOY: "Waking Moments"; et. al)
Jokes which contained sexual innuendo were said to be "dirty". One of the expectations Lewis Zimmerman foresaw for his upcoming Long-term Medical Holographic program was the ability to swap dirty jokes with patients. (DS9: "Doctor Bashir, I Presume")
In 2376, after her failed modifications to the computer core of Voyager resulted in a number of malfunctions, Seven of Nine commented to Commander Chakotay that "Clearly, Voyager is not yet ready for assimilation." When the comment failed to amuse Chakotay, she explained that it was a joke and that The Doctor had suggested that she diffuse tense situations with humor. (VOY: "One Small Step")
- "This gentleman went to see his surgeon and was informed that he needed an operation. The man thought about that and then said, "I would like a second opinion." The doctor said, "Okay, you are ugly too"."
- "You know I come from a town so small it had a fraction for a zip code. It was so small in fact that it didn't have a godfather of crime, it had a nephew."
- "I was so ugly as a child they hung a pork chop around my neck so the dog would play with me."
- "Then there was the gene bank where they crossed a lion and a parrot. They weren't sure what they got, but when it spoke, they listened."
- "Or the Human cannonball that was hired and fired in the same night."
- "And there is the one about the girl in the nudist colony that nothing looked good on." (TNG: "The Outrageous Okona")
- "Life is like loading twice your cargo weight onto your spacecraft. If it's canaries and you can keep half of them flying all the time, you're all right." (TNG: "The Outrageous Okona")
- "So he says, 'Well, I'm not really a pilot.'"
- "A man goes to a store to buy some kidneys. He says to the shopkeeper, "I'd like a pound of kiddillies, please." The shopkeeper says to him, "You mean kidneys, don't you?" The man says, "I said kiddillies, diddle I?"
La Forge didn't find the joke funny, as it was too old and Data "didn't tell it very well". Data however mispronounced the phrase "including the kidneys" after the joke was told, eliciting a laugh from La Forge. (TNG: "Code of Honor")
In late 2364, La Forge told Data a joke with the following punchline:
- "So the guy staggers to his feet and goes back to the girl. She smiles, looks him straight in the eyes and says: "Just try that in hyperspace!"." (TNG: "Conspiracy")
- "You heard the old story about the man who goes to his doctor? He says: "It hurts when I raise my arm like this!" The doctor says: "So don't raise your arm like that!"" (TNG: "Brothers")
- "Then just as the headsman swings the axe and the blade is about to fall, the count says: "Wait, wait, I'll talk!", but it was too late. And the moral to the story is: Never hatchet your counts before they chicken."
- "...and then she said: "If they're not squirming, we won't eat them.""
"Mr. Tricorder" was a joke made by Data in 2371 aboard the Amargosa observatory following the installation of his emotion chip. He used a tricorder like a hand puppet and talked to Geordi La Forge. (Star Trek Generations)
One humorous punchline Data recalled, in 2371, from the Farpoint Mission, after the addition of his emotion chip was: "The clown can stay, but the Ferengi in the gorilla suit has to go." (Star Trek Generations)
Quark once told Morn a joke that had the punchline, "And, so, the Andorian says: Your brother? I thought it was your wife!" Morn didn't get the joke immediately, and Quark re-emphasized "...wife" once again, and Morn finally got it and gave the joke a good belly laugh. (DS9: "The Nagus")
Department of Temporal Investigations agent Dulmur asked if Sisko was making a joke when he said his story might take some time. Fellow agent Lucsly backed him up and Dulmur added that they hated those. (DS9: "Trials and Tribble-ations")
IN 2375, Tom Paris told Tomin two jokes: How do you bend a hologram's ear? Use a prism. What did the counselor say to the hologram? You're projecting. These jokes prompted him to declare humor a "revelation". (VOY: "Someone to Watch Over Me")