Practical joke
A practical joke or a prank was a trick played on someone in which humor was derived from the victim's embarrassment or discomfort. They were called "practical" jokes because they were practiced, instead of being related in oral or written form. The person who performed the practical jokes was called a practical joker. According to Kirk, "the worst thing you can do to a practical joker is to play a practical joke on them." () Tom Paris and Michael Rostov were known practical jokers. (; )

Childhood
In 2237, the Vulcan healer was reluctant to answer a young Spock's request that he help I-Chaya, having heard rumors of the child's tendency towards practical jokes. The boy admitted that he had played one two years ago, but that this wasn't one. ()

After suffering from Trelane's pranks, James T. Kirk compared them to actions he erroneously assumed Spock had performed in his youth ("Dipping little girls' curls in inkwells. Stealing apples from the neighbors' trees. Tying cans on-") Upon seeing Spock's look of dismay, Kirk realized who he was talking to and asked him to forgive him. ()

Starfleet Academy
Practical jokes were known to occur at Starfleet Academy.
During his time at the Academy, Captain James T. Kirk fell victim to one practical joke after another at the hands of Finnegan, an upperclassman. Kirk later recounted the types of pranks Finnegan was prone to play (always on Kirk), explaining, "He's the kind of guy to put a bowl of cold soup in your bed or a bucket of water propped on a half-open door. You never knew where he'd strike next." ()

During Wesley Crusher's first week at the Academy, Cadet Adam Martoni reprogrammed Crusher's sonic shower to cover him with mud. Crusher returned the favor by somehow rigging an anti-matter regulator to spray chili sauce (presumably) on Martoni. ()

Lieutenant Commander Data fell victim to several practical jokes during his Academy years. ()

Aboard Enterprise NX-01 
In 2152, Travis Mayweather pranked Hoshi Sato by claiming he'd found a new lifeform that he thought might be sentient and by alleging that the captain needed her to figure out how to communicate with it. In reality, it was strawberry gelatin. Hoshi recalled this when identifying his supposedly dead body, saying she thought that his death was another practical joke. ()

Aboard the Enterprise 
In 2270, the main computer of the , which was infected with highly charged subatomic particles, played a series of practical jokes on the ship's crew, including: 

 Giving the crew trick glasses and flexible forks at dinner time 
 Replacing Spock's console eyepiece with a double-eyed one that left black marks around his eyes 
 Causing the food synthesizer to spit out piles of food at Montgomery Scott  
 Writing "Kirk is a jerk" on the back of the captain's fresh uniform shirts 
 Creating a fog and icing a deck
 Locking Leonard McCoy, Hikaru Sulu and Nyota Uhura in the recreation room 
 Trapping them in a pit
 Switching to a freezing cold blizzard holoprogram
 Reversing the gravity to keep Scotty from accessing the computer controls
 Releasing nitrous oxide onto the bridge
 Scaring attacking-Romulans with a 

To get rid of the particles responsible for the computer's malfunction, Kirk played a practical joke of his own, by saying he was petrified of going through the energy field again. The computer promptly diverted them there, clearing the particles from the ship. The Romulan warships, having followed the Enterprise through the field, began experiencing similar computer malfunctions. ()

Aboard the Enterprise-D 
In 2367, Jake Potts pretended that his brother Willie had killed him with a toy laser pistol by popping a balloon filled with red pillion dye. This prank backfired when Willie hid and ate a cove palm fruit, thereby infecting himself with a dangerous parasite. Later, when asked by Doctor Beverly Crusher if he'd ever pulled a prank on someone, Willie said he hadn't, explaining that he didn't think it was funny to be tricked like that. ()

On Deep Space Nine

In 2371, Julian Bashir dismissed Jadzia Dax's sudden outburst of passion towards Benjamin Sisko as a practical joke. ()

In 2372, Jadzia had broken into Odo's quarters four times while he was regenerating and moved all of his furniture a few centimeters out of place in various directions. Odo found her pranks annoying, and accused Quark of being in on them. Later, he personally saw to it that she fixed her changes, adding that he wanted her to promise that she'd stay out of his quarters while he was gone. She agreed. ()

In 2375, Miles O'Brien mistook the recurrence of the first line of A Tale of Two Cities on the 294th page as a practical joke of Ezri Dax, who had loaned the book to Bashir. Instead, it was proof that they were still inside Luther Sloan's mind, as neither man knew what the rest of the book was. ()

Aboard Voyager
In 2373, Tom Paris was dismayed by the unfinished status of the holonovel "Insurrection Alpha", wondering out loud if it was someone's idea of a practical joke. ()

At some point before Tuvok's promotion to Lieutenant commander in 2374, Paris and Harry Kim rigged the security console on the bridge so that every time Tuvok accessed the internal sensors, the message "live long and prosper" would play, which he had to put up with for the rest of his shift because, to his frustration, there was no one available to fix it. He would discover after his shift that the replicator in his quarters had been rigged the same way when ordering Vulcan tea. ()

In 2376, B'Elanna Torres initially dismissed Seven of Nine's conspiracy theory about Starfleet plotting with the  as a "Borg practical joke". ()

Also that year, to calm the Fair Haven holographic characters, The Doctor (as Father Mulligan) claimed that Paris and Kim pranked them, and that they were not spirits responsible for turning Maggie O'Halloran into a cow. ()

Tom Paris was also initially accused that year of altering one of Tuvok's holoprograms by putting pajamas on the Oracle of K'Tal, though he was innocent. ()

In 2377, when B'elanna Torres told Paris that she was his new co-pilot for the , he mistook it for a practical joke. ()

Elsewhere
In 2377, Doctor Lewis Zimmerman reconfigured The Doctor's tricorder so that when he performed a mitochondrial scan, it would show readings for a Vulcan marsupial. The Doctor didn't figure out what had happened until an hour later. He was all prepared to leave Jupiter Station until  assured him that he was making progress after all, as Zimmerman only pranked those he liked. ()

Alternate reality
In 2258 of the alternate reality,  mistook 's promotion of  to first officer in his absence for a prank, pleading confusion over the complexities of such practices. ()

Related links 
 Fork
 Itching powder
 Trick glass

External link 
 
Communication