These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Accidental Innuendo: For some reason, a guy just can't seem to go on a boner themed crime spree without people giggling about it decades later.
In my Pre-Flashpoint I have repeatedly established myself as the most psychotic and evil villain that Batman has ever faced. A Monster Clown with a Multiple Choice Past, my madness has made me commit every crime there is, from the laughably absurd to some of the most horrifying atrocities imaginable; everything I do is based on what my allegedly disturbed sense of humordeemsfunny. (Hey, what you call disturbed, I call creative!) Over the course of my long career I have: crippled Barbara Gordon and tried to psychologically torture her father into madness; sold nuclear weapons to terrorists, savagely beat Jason Todd with a crowbar, then killed him and Jason's mother with a time bomb; repeatedly emotionally and physically abused my girlfriend, Harley Quinn, going so far as to try to kill her multiple times; attempted to infect the entire world by poisoning the atmosphere with Joker-venom when I believed I was dying; tried to kill every newborn baby in Gotham in order to break the city's spirit, killing Commissioner Gordon's second wife, Sarah Essen, in the process; and in the Emperor Joker storyline stole the powers of Mister Mxyzptlk, becoming a nigh-omnipotent god-like being who turned the world into a hellish caricature of itself, tortured Batman to death only to revive him and repeat the process continuously until Batman was driven insane, devoured everyone in China, and attempted to wipe out all of existence. Normally without any superpowers to speak of, through sheer force of will, sadism, and an overwhelming desire to gain his nemesis's attention, I have managed to murder thousands of innocent people, endangered countless more, and earned the honor of being a monster so vile that even other supervillains scare themselves by telling tales of his exploits.
After New 52 the storyline Death Of The Family has proven that I am as monstrous as ever. Starting by attacking the Gotham City Police Department to retrieve the face I had cut off, I murder nineteen police officers and threatens to kill Mayor Hady. I instead opt to kill Hady's police guards. Reenacting old crimes, I attempt to poison Commissioner Gordon and blow up the Gotham reservoir. I hunt down the whole Bat-Family, trapping them in the Batcave and leaving them soaked in gasoline while I force Batman to watch. I attempt to set them ablaze before Batman stops him, but I leave a contingency: my special Joker gas to force them to kill one another if not for their Heroic Willpower. I show how terrifying I can be when I decide to cut loose and am defined by my twisted obsession with and desire to hurt Batman.
My Jack Napier incarnation from Batman. Even before my transformation, I was outright horrible: I was the one who murdered Bruce Wayne's parents, and if my accomplice hadn't yelled at me to get out of there, I would have killed young Bruce as well. From that to present day. For starters, I intended to poison all the Gothamites with Smylex Gas for no other reason than my own amusement, has three mob bosses killed (even joking about their deaths, at least one of which qualified under Nightmare Fuel, where I electrocute him with enough voltage to turn him into a charred skeleton after claiming that shaking his hand will be the end of it if he refuses to agree with me). I also horrifically disfigure my girlfriend Alicia Hunt and it was also implied that I threw her off a building later on in the film under the guise of suicide to free myself for Vicki Vale ("You can't make an omelet without breaking some eggs."). I gas an art gallery full of people to death just to have some "alone time" with Vicki Vale and put the components of Smylex into different cosmetics to cause random city-wide deaths just to make the people panic. I even cold-bloodedly guns down my best and only friend, Bob the Goon, just to vent his anger over Batman ruining the above attempt to gas everyone at the parade.
In Batman: The Animated Series I am the only supervillain from Batmanís Rogues Gallery who possesses no sympathetic or redeeming qualities whatsoever. Prior to becoming a supervillain, I was a mobster and hit man who murdered Carl Beaumont, the father of Andrea, over money owed to my employers. I committed this murder even after the debt was repaid. This set in motion Andrea becoming the supervillain Phantasm and took away Batmanís one chance of a normal, happy life. Following his transformation into the Axe Crazy Joker, I now commits crimes more often For the Evulz than for any profit. Samples of my crimes include repeatedly abusing my girlfriend Harley Quinn, trying to bomb a childís birthday party, setting up Catwoman to go through a grinder, psychologically tormenting Charlie Collins for two years, murdering countless people with Joker venom, attempting to drive 70 million people insane by having AceMind Rape them, attempting to nuke Gotham City, and going on a rampage with a Kill Sat. My most widely recognized crossing of the Moral Event Horizon (pictured) was from Batman Beyond: Return of the Joker when I tortured Tim Drake into insanity and implanted a microchip in the child so I could take over his body and perform a Post Mortem Comeback.
My incarnation from The Batman. Once I was a man who wanted to make people laugh, but I fell into a vat of chemicals and became an insane, murderous Monster Clown and Batman's Arch-Enemy. Devoid of any empathy—and why not? Empathy is for losers!—I commit crimes I views as "jokes" at the expense of Gotham. Terrible things I've done include poisoning people with my deadly laughing gas; putting people in various death traps; torturing Detective Ethan Bennett for hours and causing Bennett's mutation into Clayface; impersonating Batman and gassing people for minor crimes; using Bane's venom to go on a rampage; attempting to drop a teenage boy into a vat of chemicals; frequently mistreating his henchman and my girlfriend Harley Quinn, as well as abandoning them to be arrested or even to die; and filling the abandoned tunnels and mine shafts beneath Gotham with miles of dynamite to collapse the city to oblivion. That I manage to qualify despite being toned down to all get-out is a testament to how delightfully twisted a person I am.
Fandom Rivalry: Apparently, some of you people are beating each other to death over whether Mark Hamill or Heath Ledger is the better me. Get over it! Don't you know what I am? Either of them is perfectly fine and dandy as a valid me!
"Funny Aneurysm" Moment: Oh, aren't they all? Though reading about those times when others have tried to steal my idea of copyrighting a lifeform of my own design had me giggle. If someone as clever and handsome as me couldn't pull it off, what makes them think they can? Wait, what do you mean, theydid?!
Ho Yay: I did have that fling with one of my mooks in "The Devil's Advocate" now, didn't I... And he's lucky just his legs got broken.