Jerkass: Practically everyone in the show at some time or the other, with Mr. Krabs and Squidward being the most prominent examples.
In "Keep Bikini Bottom Clean," a cop follows Squidward around and continuously slams tickets into his face for even being near a pile of garbage.
Patrick becomes one of these any time he gets a taste of power or some sort of reassurance of his "genius" abilities. (The episode where he gets a boat, when he becomes king, the time when his parents come over, etc.) Any other time, he's just The Ditz taken to its Logical Extreme.
Even the normally sympathetic Mrs. Puff becomes one in "Demolition Doofus" as she tries to outright MURDER Spongebob!
Joins To Fit In: Squidward's whole reason for leaving his own neighborhood and moving to Tentacle Acres.
Journey To The Center Of The Mind: The dream version in the episode "Sleepy Time." Naturally, Spongebob managed to ruin the dreams of everyone in Bikini Bottom, and he awoke to find a group of annoyed friends and neighbors, insisting he stay out of their dreams because they get enough of him during the day.
Just Friends: SpongeBob apparently has a crush on Sandy. This isn't very noticeable within the show itself, but supplemental materials place special emphasis on it. A survival guide released in 2002 played with the fact, hinting at the crush being "secret"◊.
Sandy's official biography states that she "is the only thing under the sea that SpongeBob likes better than his job at the Krusty Krab."
Karma Houdini: These have popped up from time to time. Probably the most notable is Granny from the episode "Have You Seen This Snail?".
Kitschy Local Commercial: When Mr. Krabs decides to make a commercial for the Krusty Krab, Squidward initially goes all out to make it as extravagant as possible. Krabs then decides it's too much and goes for a cheesy commercial on at 3AM.
Knight of Cerebus: Granny from the episode "Have You Seen This Snail?". She, unlike other recurring villains in the series (including Plankton and Mr. Krabs, who is considered funny in his actions even more deplorable), she contrasts absolutely comical traits, and the episode itself made things very serious. Later, she revels who killed all the snails to eat them!
Surprisingly, Plankton manages to one in the same movie
Knight Templar: Mr. Krabs's increasingly less provoked antagonism towards his rival Plankton. While in early episodes, Krabs was interested solely in protecting his own business from the latter's villainous tactics, he became more obsessed in actively destroying any minor success or happiness Plankton achieved out of spite, via unscrupulous methods or not. On occasion Krabs is shown to take offense when Plankton merely isn't suicidally miserable. SpongeBob often plays a role in this as well, albeit due to his naivete and on-off friendship with Plankton, likely more as a blind follower of Krabs than out of spite.
Knows A Guy Who Knows A Guy: Spongebob tries to warn Squidward. "Sea Bears are no laughing matter, why, once I met this guy who knew this guy, who knew this guy, who knew this guy, who knew this guy... who knew this guy, who knew this guy, who knew this guy's cousin-"
In "The Suds", Patrick tells SpongeBob of the horrors of the doctor's office which he knows because "I know a guy who knows a guy who went to the doctor once".
Lampshade Hanging: The series features phenomena impossible in its underwater setting, like fire, and the characters comment on this.
"Hey, if we're underwater, then how can there be a-" *fire extinguishes*
In one episode, a tree is shown wearing scuba gear.
In "Chimps Ahoy", Sandy's bosses come to visit her and check on her scientific progress. One points out that sending scientists underwater to live in Treedomes for no reason doesn't really make much sense.
Then there's the infamous episode where SpongeBob breaks his butt and becomes agoraphobic. After several attempts to get SpongeBob outside, a gorilla suddenly attacks Patrick, Sandy, and SpongeBob, who points out the absurdity of having a gorilla underwater. Unable to explain itself, the gorilla rides off on a zebra into the sunset. The last shot is a family watching the episode, being just as confused as we are.
In "Squilliam Returns" SpongeBob has to forget everything he knows except fine dining. This is visualised by little SpongeBobs in his brain shredding documents, burning them, etc. One of them asks his boss why he should work harder, as they're just "...a clever visual metaphor used to personify the abstract concept of thought." When the boss then threatens to fire said worker he's begging for him not to, because he has wife and kids. Which kind of qualifies as a lampshade hung onto a lampshade.
Last Day To Live: Inverted — the titular sponge is thought to have unknowingly eaten a deadly pie, which will end his life at sunset. Squidward, responsible for bringing a pie-shaped bomb to SpongeBob, feels guilty enough to spend the rest of the day doing anything SpongeBob wants. It's eventually revealed that SpongeBob never ate the bomb-pie, but rather a different pie. He saved the bomb, which he promptly trips and thus throws into Squidward's face, producing a nuclear blast.
Laughably Evil: Dennis, Plankton's Assassin from The Movie, is downright sadistic and threatening. He's also very entertaining to watch due to his over-the-top nature and constant Evil Laugh.
Laughing Mad: SpongeBob engages in a bit of this during the infamous "I've Been Waiting for You, Patrick" scene from "Bummer Vacation".
Laugh with Me: A variation. The Flying Dutchman take SpongeBob and Patrick onboard as his crew. When he demands that they "howl with me, that we might set the seven seas, ABLAZE with fear!", they comply with various ridiculous noises, until he finally gives up on making them scary.
Light Bulb Joke: The basis of many of SpongeBob's "squirrel jokes" stand-up.
SpongeBob: How come it takes more than one squirrel to screw in a lightbulb?
Audience: BECAUSE THEY'RE SO DARN STUPID!!!
Line-of-Sight Name: When the Flying Dutchman comes for Mr. Krabs' soul in the hospital, Mr. Krabs insists that he is "Harold Flower", after the flower on the end table.
It becomes even funnier in the German dub, where he claims to be be "Benjamin Blümchen" (Benjamin Flower), the titular character of a popular German children's cartoon about a talking elephant. Both Benjamin and Mr. Krabs have the same voice actor, making this kind of an Actor Allusion
Loud of War: There's a jellyfish party at SpongeBob's that's been going for 18 hours that annoys Squidward, so he turns his house towards SpongeBob's and plays his clarinet through full-blast speakers. The jellyfish are not happy.
Lying Finger Cross: Played with in one episode. When SpongeBob and Patrick promise Mr. Krabs not to play on the fishing hooks, Patrick claims he had his fingers crossed. SpongeBob then points out that Patrick has no fingers.
Made Out To Be A Jerkass: In the infamous "Stuck In A Wringer", Patrick's stupidity results in SpongeBob being trapped in a wringer and can't get out, and despite Patrick trying to convince him otherwise, nothing goes right for him anymore. Finally, at an amusement park, SpongeBob yells at Patrick, saying it's all his fault his life is ruined. After a sad Patrick leaves, the crowd around SpongeBob get on his case.
Man Child: SpongeBob's actual age is very difficult to guess. He lives independently, has a job, is trying for his "boating license"...and acts like a five-year-old with ADHD despite being 25.
Marshmallow Dream: SpongeBob dreams of eating Krabby Patties and wakes up chewing on his pillow.
Also referred to on "Sleepy Time". When SpongeBob meets Gary in the dreamworld, the now erudite Gary tries to explain to him the concept of dreams as a view to another world. When an Emily Dickinson poem goes over SB's head, Gary recites one more his speed: "There once was an old man from Peru; Who dreamed he was eating his shoe; He woke with a fright; In the middle of the night; To find that his dream had come true".
SpongeBob has a cameo in "Peter Kay's Animated All Star Band", a Children In Need music video crossing over many significant British Stop Motion cartoons, a few 2D British and American cartoons, and the live-action Teletubbies. (The reason for having a mere cameo is that the 2D shows* Including a character from Nickelodeon's "other side", just as the Children In Need telethon includes programmes from The BBC's "other side". Funny, no? only appear on TV screens to avoid major Medium Blending.)
Meat O Vision: Subverted in "Fear of a Krabby Patty", where SpongeBob develops a fear of Krabby Patties, and sees Mr. Krabs and the customer as them.
Medium Blending: Above the surface of the water, everything's in live-action.
Merchandise Driven: In-universe example in "The Krusty Sponge". When SpongeBob's cooking was the sole thing that saved Krabs from a bad review from a food critic, he exploits that for as much as possible with many SpongeBob-themed items, including the Spongy Patty... even though they were rotten.
SpongeBob: If Krabby Patties are illegal now, aren't we breaking the law? Mr. Krabs: There's an old saying, lad. What doesn't kill ya... usually succeeds in the second attempt. SpongeBob: But what does that have to do with making Krabby Patties? Mr. Krabs: Nothing!
The Millstone: Patrick fits more than the usual. Whenever SpongeBob or anyone has a plan, Patrick is sure to screw it up, or do something stupid to make it worse.
Mirror Cracking Ugly: SpongeBob thought he was this, but it was just his reflection reacting to his smelly breath.
Mondegreen: "Sweet Victory" from the episode "Band Geeks" has a few lyrics that are often misheard, specifically "the world closing in" being heard as "the wind closing in", "be on the attack with your wings in the wind" being heard as "they only attack with their wings in the wind", and "the games will begin" heard as "the daydream begins"
Moving the Goalposts: Kevin's treatment of SpongeBob in "I'm Your Biggest Fanatic". SpongeBob is trying to get into the Jellyfishers' Club, but their leader Kevin keeps stringing him along with increasingly difficult tasks, at which SpongeBob succeeds with ease. When they finally come up with something sufficiently impossible, it winds up in Kevin being Hoist by His Own Petard as the fake "queen jellyfish" he creates attracts a real king jellyfish, and SpongeBob saves the day, revealing Kevin as a complete loser.
Mr. Imagination: SpongeBob and Patrick create a world of scenarios with only a cardboard box in "The Idiot Box", much to Squidward's disbelief.
Multiple Endings: "Shanghaied" has three (depending on whether SpongeBob, Patrick, or Squidward gets the third of Three Wishes), which viewers got to call in and choose between during the episode's premiere. Reruns of the episode show only the winning ending, though all three endings are available on some home video releases.
In the episode "Procrastination". As the name implies, SpongeBob grapples with his denial for hesitation in writing a 800-word essay. In one of his many time-wasting gimmicks, he spends an implied ludicrous amount of time and effort writing the "The" at the start of the paper, so the sequence ends up just looking "awesome" instead of being the Hard Work Montage it initially appears to be.
The opening scene of The Movie features a dramatic scene based around the "crisis" of a customer being given a Krabby Patty without cheese, complete with a slow-motion sequence of SpongeBob putting some cheese into the patty. It's a Dream Sequence, but still...
How about any time the Krabby Patty is brought to the audiences attention by SpongeBob, or at least when it focuses on him making Krabby Patties?
When a customer gets a Patty with jellyfish jelly added, he's so enthused that he bursts into an impromptu musical number: "LISTEN to me, everybody! I just had a sand-wich! It's no ordinary sand-wich!"
And in one of the "Legends of Bikini Bottom" episodes, SpongeBob is unconscious due to his Krabby Patty meter being empty. Mr. Krabs gets him to eat one. He then blasts up, explodes into pieces, then regenerates after all of them land together, and then... "OHHHHHHHHH, YEAHHHHHHHHHHHHH!!!!!!!!!"
Mermaid Man. "To the meatloaf... AWAY!"
Mermaidman and Barnacleboy's origin story (specifically, that they gained their powers from eating some overcooked popcorn)
Mundane Wish: The episode "Shanghaied" had Patrick waste the first wish the Flying Dutchman gave him and SpongeBob on wishing that he knew about the wishes earlier. In one of the alternate Multiple Endings, Patrick used the third and final wish on a pack of gum.
My Master, Right or Wrong: SpongeBob, despite his occasional disgust at Mr. Krabs's actions and sympathy for the people he victimizes, (even Plankton), generally follows through with his plans blindly, either due to his blind idolization of his boss or the fact his dream job may be at stake otherwise.
Negative Continuity: Hoo boy. Except for Help Wanted and The SpongeBob SquarePants Movie being first and last in the series respectively (confirmed by Word Of God), there's no revealed order or canon for any of the other episodes. Spongehenge, despite being in season five, must come before many other episodes because SpongeBob specifically says that he's never been late for work when in fact he has been in earlier episodes. Just One Bite (a season three episode) also must happen after many episodes in the series due to Squidward remarking multiple times that he doesn't eat at or like the food at the Krusty Krab.
The show also ignores what it said earlier. In a recent episode, Patrick's sister comes by. All fine and good, except in a previous episode (previous being a LONG time ago), Patrick talks quickly about being ugly (his breath just stunk), and one of the things he says is "and if my sister finds out, oh wait I don't have a sister..."
He states in the episode that she's his long lost sister who he just found out is still alive.
Inverted Trope in the episode, "Your Shoe's Untied." Spongebob has not needed to re-tie his shoes in so long, he has actually forgotten how to do so.
In the episode "Pickles", SpongeBob goes through a Heroic BSOD when he thinks that he got an order wrong. It gets so bad that he starts wearing his pants on his head and speaking in scrambled sentences. Mr. Krabs figures that if he can get SpongeBob to make a Krabby Patty again, then he'll go back to normal; he even compares it to riding a bicycle, then notices a bicycle on a boiling pot in SpongeBob's stove.
Never Say "Die": Lampshaded in "Squidward the Unfriendly Ghost": SpongeBob thinks he killed Squidward and says, "I don't know how to say this, but our friend Squidward, he's... pushing up daisies!" Patrick calmly replies: "Oh, I thought he was dead."
No Fourth Wall: Any episode involving Patchy the Pirate acknowledges that SpongeBob is a just a show. Other episodes do this as well, such as showing a live family reacting to the Mind Screw ending to the episode and shutting off the TV.
No Good Deed Goes Unpunished: The episode "Can You Spare a Dime?" features Squidward quitting his job over a misunderstanding. When he ends up losing his house, Spongebob selflessly takes him into his own home, and takes care of him. Squidward "thanks" him by becoming a freeloader, forcing SpongeBob to wait on him hand and foot.
Barnacle Boy: Listen, bignose. That guy's been saving your butt since before you were born. Don't you have a living legend discount or something? Squidward: This is a restaurant, not a lending library. And who are you calling bignose,bignose?
Off Model: Happens frequently in season one. Squidward's head size often changes from shot to shot, and there is something "off" about SpongeBob's appearance during the first few minutes of "Tea at the Treedome".
Out of Focus: Sandy, Larry, Mrs. Puff, and a few other recurring characters don't appear as often in later seasons to the point where they are forgotten as characters. It's also driven to the point where they forgot Sandy's name in one episode (she's referred to as "Sandy Squirrel" in "Keep Bikini Bottom Beautiful").
And Flats the Flounder, if you know that it's Biff Tannen voicing him.
Davy Jones' Locker is really guarded by The actual Davy Jones, complete with "Daydream Believer" in the background.
In the episode "Missing Identity", when SpongeBob imagines the bank robber entering the store with his name tag, the robber yells "ATTICA!".
A musical bonus: In the episode where Patrick becomes smart when he switches his brain with brain coral, he mentions a clarinet piece by "Cornelius Bumpfish". Someone on the writing team must like Steely Dan, whose clarinetist was a man named Cornelius Bumpus.
Pet the Dog: The ending of "Love That Squid", where Squidward, after seasons of being down on his luck and designated to have anything seemingly good that could happen to him get crushed, succeeds in getting a date with a girl.
Pie Eyed: In the 10th Anniversary episode, Patchy shows a SpongeBob short in a 1920's style where everything has this eye style.
This happened to the Flying Dutchman TWICE. Once was when he tried to enslave Patrick and SpongeBob (they made horrible minions) and another time was when he bought SpongeBob from Mr. Krabs (SpongeBob was too annoying for him to keep).
Plot Sensitive Latch: In the episode "Krabs Vs. Plankton", Mr. Krabs is sued by Plankton for slipping in the Krusty Krab, and his lawyer is indisposed, giving SpongeBob his briefcase, which he claims contains everything necessary to win the case. Unfortunately, the lawyer neglects to tell SpongeBob the combination to the lock, so he spends most of the trial struggling to open it. At the last possible moment, the briefcase opens, revealing a Krabby Patty, which is used to lure Plankton out of his ruse and lose the trial.
Pooled Funds: Squidward does this on a pile of Krabby Patties after he becomes addicted to them. Mr. Krabs does this with money.
Prison Episode: "The Inmates of Summer" where SpongeBob and Patrick get on the wrong ship and end up on a prison island. Complete with a character voiced by R. Lee Ermey!
Pro Wrestling Episode: "Krusty Krushers," with Mr. Krabs as SpongeBob and Patrick's manager in a tag match against two HUGE opponents in the hopes of making big money. The opponents totally squash SpongeBob and Patrick until their double-team diving headbutt collides with Patrick's iron butt. SpongeBob and Patrick have the choice of either $1 million in cash, or a chance to go to Wrestle Camp. To Mr. Krabs' dismay, they choose Wrestle Camp.
Produce Pelting: Squidward is hit with tomatoes during his ballet skit in "Culture Shock".
Pseudolympics: The Fry Cook games, including events such as patty throwing, artistic ice cream diving, bun wrestling...
Psychopathic Manchild: Squidward. While most of the time acting serious, often several times behave very childish way, ultimately the childish behavior becomes a dangerous madman. And no doubt, the clearest example for this is in the episode "Fools In April".
Plankton also may count. It was in the early seasons an evil enemy, especially as he is seen in the film, but at least as seen in the episode "FUN", seems to have pretty a childish side with SpongeBob when he befriends him. And it is assumed that Plankton is almost as old as it is Mr. Krabs.