There was a Second Edition sourcebook called Dirty Secrets of the Black Hand which proved very unpopular because it suggested that the Sabbat (Already a secret vampire conspiracy to control humanity) was itself controlled by a secret conspiracy within the Sabbat's "Black Hand" faction, which was itself called the Black Hand. This "True Black Hand" controlled everything from the land of the dead, residing in the ghost of the First City mankind founded. There are more details, but things only get more needlessly complicated and stupid from there. When the next edition of Vampire: The Masquerade came out, they scaled back the bloodlines introduced in that book to about a dozen members each, declared that the scope of the "True Black Hand"'s power and agenda were extremely exaggerated, and then dropped a ghost atomic bomb on the underworld city they were operating out of for good measure.
The True Black Hand got brought back in V20, scaling back their ability to influence events, retconning certain of their more egregious aspects so they were more appropriate to the setting and/or optional, and showing that the truth of many of the potentially setting-shaking secrets they were sitting on was unclear even to them.
The Values Dissonance of the first edition and early second edition's treatment of the Romani was swept under the rug by retconning their association with the Gangrel and wiping out the Romani-inspired Clan Ravnos in the metastory.
Broken Base: A number of scandalous events surrounding the upcoming 5th edition of the game, such as hiring an infamous harasser to write their first digital release and a player character in the 5th edition playtest document who was seen as a pedophile by fans, have resulted in a good portion of the fanbase turning against the post-Paradox buyout White Wolf.
Sascha Vykos, born Myca Vykos, is a monster whose legacy dates back to 11th Century Constantinople. Sired by the Tzimisce Symeon, Vykos eventually destroyed his sire by repeatedly consuming and regurgitating him before a final act of draining him to death. Changing his gender and taking the name "Sascha," Vykos became a major figure in the monstrous Sabbat, feared even by its monstrous Clan. Vykos invents new tortures, having perfected them upon countless unwilling victims whose agony it can prolong for years to centuries, alternating it with incredible pleasure to make the victim unsure if it is experiencing torture or rape. In modern times, Vykos plays a major role in the war for the United States East Coast, using its fellow Sabbat as Cannon Fodder or torture victims when it's bored. One luckless failed assassin is reshaped to its servant, tortured and broken so she may experiment with how loyal it has made him. With a thousand-year reign of horror, an insatiable hunger for knowledge and an unspeakable appetite for torture, Vykos is the one who shows the rest of the Sabbat what it truly means to be a monster.
Augustus Giovanni, the Giovanni Antediluvian, is the most selfish and monstrous of his clan and family. A mortal merchant sired by the Antediluvian Cappadocius, Augustus masterminded the Conspiracy of Isaac to create enough chaos to murder and Diablerize his own sire before exterminating the entire Cappadocian clan. Using his own family to become new members of the Giovanni clan, Augustus left the mortal bloodline intact, crafting his family into incestuous, cannibalistic necromancers who regularly enslave the dead and scheme and backstab for his favor and the honor of being Embraced (turned into a vampire). Desiring to supplant God himself, Augustus enslaves countless wraiths to eventually destroy the Shroud and cause the world to be utterly overrun by the dead so he can enslave both the living and the dead and become the unquestioned master of everyone.
Nergal, one of the three founders of the Baali bloodline, manages to stick out even by their standards. Almost solely responsible for turning the Baali into a Religion of Evil so vile that they make the Followers of Set seem tame by comparison, Nergal ruled a city in ancient Mesopotamia as a king and unleashed a plague on his own people in an attempt to awaken a sleeping Eldritch Abomination. Moloch, another of the clan's founders, realized just how bad of an idea this was, and actually sold Nergal out to the other clans in a desperate attempt to stop him. Nergal, of course, survived, attempted the same ritual again, and when that failed, went to the New World and declared himself a God to the Aztec people, who named him "Huitzilopochtli." He went on to establish a particularly brutal practice of blood sacrifice and human sacrifice. When the Lasombra-led Spanish Conquistadors showed up, Nergal casually sold his followers out and went into torpor beneath what is now Mexico City, where he remains to this day. Even in the present, the surviving descendants of Moloch seek to stop Nergal and his descendants from breaking the world by creating Hell on Earth. How bad Nergal is can be demonstrated by the fact that nearly half of a bloodline universally regarded as the most malevolent in the entire setting thinks he's a menace and needs to be stopped.
Quite a bit of the Ravnos clanbook was snarking at the others. Comes of being a clan of jokers to start with and then having little left to lose after the Week of Nightmares.
There's a Mental Flaw, "Stereotype", that makes you act as a camp vampire (accent, cape, the works). Stereotype returned in V20, but in addition to the typical Bela Lugosi homage, this flaw can now also cause you to want to cover your skin in body glitter.
Evil Is Cool: Supposed to be subverted. However, some writers play it straight, usually with some of the most atrocious Clans.
The Russian part of the fandom tends to refer to Old Clan Tzimisce as "Zimischi". The clan's original name is just as unpronounceable in Russian as it is in English, and the Old Clan faction is canonically prominent in Russia - so it needs a Russified name, and Zimischi it is. It means something like "Great Winters". Most use a different transliteration for the Sabbat Tzimisce ("Tsimiskhi" is the most common). So there is Tsimiskhi the Sabbat clan, and Zimischi the Independent clan.
Memetic Badass: Smiling Jack, even in the pen-and-paper game. A Brujah ex-Pirate who has no problems getting with the times.
The prose introduction for the Baali clanbook features a supposedly respected abbot having sex with a preteen boy. After a few minutes, misshapen maggots begin crawling from inside the boy straight up the man's urethra as the boy, a Baali vampire posing as a mortal, clenches down with his knees to prevent the man from escaping, breaking several ribs in the process as the maggots begin burrowing, feeding, and laying eggs in his abdomen. This is only part of how the Baali choose their new initiates. At this point, you can stop reading now and count yourself lucky.
The original Clanbook Tzimisce. The illustrations look like what might happen if H. R. Giger and Salvador Dalí had been fused into one person. Which, come to think of it, is something at least one Tzimisce probably thought about doing.
Out of Focus: If you read the first or second edition rulebook, you'll get the idea that the game is a power struggle between the Brujah, anarchs, and young vampires in one camp and the Tremere, Toreador, Ventrue and elders in the other. Everything encourages player characters to be heavily invested in the conflict. As the Metaplot progressed, the Tzimisce, Setites, and the Salubri gradually took over the narrative; out of the initial big four only the Tremere retained their relevance right to the end (and mostly because of their connection with the Salubri founder, Saulot).
True Art Is Angsty: In many ways, Vampire: the Masquerade (along with Warhammer) created the Darker and Edgier movement]] of today, and is the original Gothic Horror game of the 90s. The nihilism of Generation X and the associated rise in popularity of the Goth subculture is what gave force and shape to this setting. It was so dark and bleak at its peak that Castle Falkenstein and many other tabletop games were created specifically as an escape for role players who didn't want a dark, soulless, brutal game every time they touched a die.
Values Dissonance: In early editions, Romani people are treated as an entire culture of irascible thieves, possibly influenced by their representation in Gothic literature and classic monster movies. Ravnos, a clan rooted in Romani culture, is explicitly a clan of criminals, tricksters and vagabonds whose members must pass a willpower check to avoid indulging in their crime of choice.
Clan Salubri's backstory is so tragic you want to hug them.
From the adventure Lair of the Hidden, there's the Cappadocian Drenis. She was born a male in the second century AD, but after being gang-raped by enemy soldiers and being unable to consummate his arranged marriage due to the resulting psychological trauma, he ran away and joined the priestesses of Cybele, having himself castrated and becoming a woman in every other way as well due to 1) being disgusted with the male gender entirely after his experiences and 2) believing he would be "in a half-state, neither a man nor woman" until he went through with it. The descriptions of the character elsewhere in the book makes it clear that the psychological scars have persisted over the centuries, even suggesting that Drenis entered into the pact with the demon out of self-destructiveness ("There are deep wounds in Drenis' psyche, a fundamentally gentle nature long subjected to horrors beyond its capacity, and so she sometimes behaves in ways no one, including she herself, can really explain"). Add to that the fact that she's one of the few good members of The Twelve (she's Humanity 7, the human baseline and second only to the senile-but-gentle mad-vampire Demetrius), and you really feel bad for her.