A family full of eccentric, weird and sometimes insane relatives. Preferably all of them, but as long as it's the majority of them then it's okay. Commonly it's all of them except one perfectly normal one.
Someone may observe their... "activities," but when they confront the family about this, the said family will often have no idea that they are considered to be out of the ordinary.
See also Big Screwed-Up Family. In the Blood is the darker version of this. Contrast Turn Out Like His Father. Compare Shared Family Quirks.
Isumi's grandmother mistakes her daughter, Isumi's mother, for Hayate when meeting him for the first time. And the mother thinks she actually is! Even wondering where she went when the grandmother changes paths.
Shinichi's father in Detective Conan is a mystery writer who doesn't investigate because he's Brilliant, but Lazy. Fellow detective Heiji's father is a well-known police investigator. Haibara's parents are scientists.
InuYasha: Compassion for humans is rare amongst youkai and it tends to cause trouble. Most youkai kill or even eat humans instead of protecting them. Sesshoumaru originally states Inuyasha's human mother infected their father with weakness and Inuyasha must have inherited his compassion from her since Sesshoumaru doesn't have any. Myouga later clarifies that Inuyasha's compassion actually comes from his father. Eventually, it becomes obvious that Sesshoumaru's not as immune as he thought, culminating in his mother observing that his compassion for humans has turned him into his father. It would seem this compassion does run in the familyresulting in Inuyasha and Sesshoumaru being Not So Different, after all. By youkai standards, that makes them fairly eccentric.
For Kakuma Keita in the anime adaptation of Inazuma Eleven, being a Large Ham Announcer runs in the family. It helps that his father is a professional TV announcer for soccer matches.
One Piece: Luffy and his father Dragon are the only known people to have declared war upon the World Government and gotten away with it. Completely unrelated to each other. Dragon is also leading an active rebellion.
In Servant × Service, as Yutaka Hasebe's sister Kaoru mentioned, the entire Hasebe family are (1) civil servants and (2) share extreme Brilliant, but Lazy / The Slacker traits. Yutaka, who as at first seen as a loser if not for his Hidden Depths, is indeed the most downplayed in terms of this trait.
The House of M, currently made up of Magneto, Quicksilver, the Scarlet Witch, and Polaris (probably), All of them pretty much known for periodically leaving their sanity at home. The third-generation kids may or may not be affected, but so far they're... mostly doing well.
Except for the ones who may or may not have just been a physical manifestation of Wanda's psychosis.
Oh, and the one who's currently being treated for an addiction to the Inhumans' Terrigen Mists.
Which her father got her hooked on after taking a few hits himself.
In All Fall Down, IQ and IQ Squared are both lonely, brilliant, irritable men who find it impossible to talk to each other.
In certain stories, we learn that Archie Andrews' ancestors were just as girl-obsessed and clumsy as he is.
This is an assumption if Sayu knew if Light was Kira and continued his work. A couple have Ryuk be her Shinigami, only one or two have Light reincarnated as a Shinigami himself.
Loz, Yazoo, and Kadaj from Final Fantasy VII: Advent Children. Like their Father, they all want to help their Mother Jenova in whatever they can. If that includes threatening Formerly Corrupt Corporate Executives, Kidnapping Children, and summoning a Dragon to destroy a City, all the better!
The House of Yes only shows four members of the Pascal family but they all have some severe issues. Not to mention that it is hinted that Mrs. Pascal killed her husband, which echos the climax of the film.
The Bagthorpes, in the children's novels by Helen Cresswell (they start with Ordinary Jack). Tess, Rosie and William are all somewhat eccentric, and their parents and grandparents might edge into mildly deranged, as might their cousin Daisy... They all (well, except Daisy) believe wholeheartedly in their genius as a family and individually, and take themselves very seriously. In one of the books in the sequence, they try to break as many Guinness World Records in a summer as they can...
And in keeping with the trope, Jack and his ally Uncle Parker are the only sane ones people can bear to have anywhere near them. Also Grandpa (though he's less developed as a character).
The Weasleys are one big kooky red-headed family who are implied to be quite old and presumably extensive, as females are very rare in their line. There's only one Squib, who Ron reveals to be an accountant.
Cordelia: Counts Vorkosigan have come to horrible ends throughout your history. You've been blown up, shot, starved, drowned, burned alive, beheaded, diseased, and demented. The only thing you've never done is die in bed.
Count Piotr, the guy Cordelia was talking to and the 10th Count Vorkosigan, was the first to actually accomplish that last one: dying in bed at an advanced age. Miles Vorkosigan (whom his mother explicitly does not think is sane) has also got a lot of other crazy people in his family tree, especially from the Vorrutyer and Vorbarra branches of the family.
Subverted in the Doctor WhoEighth Doctor Adventures novel The Taint: Fitz's maternal relatives are mostly more or less insane. It turns out it's due to alien brain slugs, which the Doctor deals with. It seems, however, that Fitz has a slightly different view of matters, as in one or two later stories, he thinks he's hallucinating and blames it on the craziness that runs in his family, even though he hasn't got a brain slug any more. Naturally, he's not hallucinating.
The Smedry family of the Alcatraz Series, in addition to having hereditary magical talents, have a reputation for extreme eccentricity.
In G. K. Chesterton's The Man Who Was Thursday, it's mentioned in passing that Syme grew up in an extremely odd family and eventually got so Bored With Insanity that he rebelled by being as sane as humanly possible. In fact, he's so sane that he's almost too sane, and therefore, in his own way, just as crazy as the rest of them.
The Woosters in Jeeves and Wooster are a pretty eccentric bunch in general, and at least one (Henry Wooster) spent his last days "in some sort of a home". For this reason, the "nerve specialist" Roderick Glossop has latched onto Cloudcuckoolander Bertie Wooster as insane and potentially dangerous.
Mary Poppins and her relatives each have at least one mystical quirk.
Arrested Development is about a family that has no idea how to live conservatively and act like decent human beings....except for Michael Bluth, who the family both counts on to keep them afloat and takes for granted.
The Munsters are all members of the Monster Mash and are considered weird... except for human-looking Marilyn - who was considered ugly by the rest of her family (though she shares some of the other members' inhumanness like her very low body temperature).
Pretty much any reality show that involves some sort of family member swap. The shows will always show families that have weird quirks and the person who is swapping into that family usually finds it disturbing.
The Winchesters in Supernatural. Hunting, making deals with demons...
LazyTown's Stephanie is the only character in the show who has bright pink hair. But according to her uncle, it's a trait that runs in the family.
Kenny's family in Kenny vs. Spenny are all pure evil. At one point the entire clan comes together to fake Kenny's mom's death and hold a fake funeral and going in mourning just to keep Spenny from winning a footrace.
The Pond family from Doctor Who is smaller than most examples, but has more wackiness than most small planets. Poor Rory seems to be the Only Sane Mannote Though you would be too if you had the memories of 2000 years of protecting Amy and nothing really fazed him any more., as his wife spent her childhood biting psychiatrists, his daughter is a self-proclaimed psychopath, and his son-in-law put the "crazy" in Crazy Awesome.
This Trope was the name of the title of an episode of Murder, She Wrote featuring Jessica's British cousin Emma (also played by Angela Lansbury); she's just as much a Doom Magnet (and just as much a sleuth) as her cousin.
Amanda Palmer's "Runs in the Family" describes people who have inherited various complications from their bloodlines (My friend has maladies/ Ricketts and allergies/ That she dates back to/ The seventeenth century) and goes on to talk about her own family.
I went back to my mother I said I'm crazy ma, help me She said I know how it feels, son 'Cause it runs in the family
A fairly minor case Played for Laughs in Dino Attack RPG. Sarah Bishop gained a particular infamy among the cast when she became the first known person to hate the Brickolinis' pizza (though Pierce might also count, or he may just have eaten a particularly hot one). Sure enough, a few posts later, it turns out her daughter Kate can't stand the taste of Brickolinis' pizza either.
The von Karma family. It's subtle, but if you pay attention, Franziska von Karma from the second game onward shares the same poses for her sprites as her father Manfred from the first game. Less subtly, both are prosecutors with obsessions for absolute perfection (and although Franziska eventually gets over it, she does maintain the no-nonsense sense of authority that had come with it).
Edgeworth is a good example of this as well in the fourth case. The outfit is very similar to Manfred's, and the fingerwag is shared by both.
Jack can dodge flying knives, grab them from the air, and throw them back at whoever threw them in the first place. He can also punch his way out of the ground.
Mom is an ex-agent who beat up Jack's dad when they first met and tried to take him hostage. She randomly throws knives at her son and puts poison in his cereal (among other things) to teach him how to defend himself from attacks both subtle and direct.
Dad is an ex-agent who almost beat up Jack's mom when they first met and she tried to take him hostage. He wears Kiss The Cook aprons, yet likes to single-handedly grab foes by the head and throw them at one another.
In Girl Genius Spark, which might be better known as Science-Related Memetic Disorder, tends to run in families. It's probably the most apparent in Heterodynes, a house full of powerful Sparks and vicious warlords, who terrorized Europa for centuries.
A possible explanation for Michael Jackson's extensive plastic surgery is because he didn't want to look like his abusive father.
The Durrell family, if youngest son Gerald is to be believed, were all amiably eccentric, with a few downright barmy older relatives. See My Family and Other Animals.
A recent rage comic meme had an extremely overweight lady visiting the doctor. The doc tells her "Ma'am, I'm afraid you're morbidly obese." The lady says "I'm sorry, but obesity runs in our family." The doc comes back with "Lady, nobody runs in your family!"