Are they some kind of Jekyll & Hyde? Not really. They're just at their best with people they choose to hang out with; having been forced into close proximity with these other people for years, without being asked, has created issues. The mere fact that they share genes with those other people doesn't remove the problem. Like most real people, they have good and bad personality traits, and their difficult family relationships bring out the bad ones. Unfortunately, while they could simply avoid any social acquaintances who annoyed them this much, nobody can change who they are related to by blood.
This is often Played for Laughs in an episodic comedy, when some broadly sympathetic character gets a visit from family and suffers intense temporary stress or turns into a monster for that one episode. In such cases, the problem usually lies with the visiting family member, who is shown to be every bit as bad as the regular character thinks, justifying the negativity; when the visitor leaves, everyone sighs with relief and the status quo is restored. However, this isn't guaranteed; some or all of the fault may turn out to lie with the regular character, whose bad side is thereby revealed, or who has to learn a lesson or resolve their issues at some point. This may happen when the visitor admits to some past error which left the regular disproportionately embittered.
Alternatively, the family may be recurring background characters, in which case, the problem probably does lie largely or entirely with them, or the lead character will end up looking unsympathetic. They may be anything from minor nuisances to recurring antagonists to pure evil. If they're all evil, this makes the foreground character a White Sheep; if they're not that bad really, the hostility becomes a significant character flaw — which may just be a way for the author to save the foreground character from being too much of a paragon. Whether relatives-by-marriage come within the scope of this trope may depend partly on whether the character considers the ties of blood to extend that far, but it can be as difficult to avoid Obnoxious In-Laws as to avoid blood relatives if your spouse feels obliged to be loyal to them and you want your marriage to survive.
As many people will probably admit, there's a lot of Truth in Television in this; some quite nice people are fully capable of squabbling harshly with some of their relatives, for good or bad reasons. The saying "We Choose Our Friends, God Gives Us Our Relations," or some variant of that, is a rueful acknowledgement of this.
This trope contrasts with Thicker Than Water, but is not the opposite. Someone can dislike their family quite intently, but still feel that blood relatives have an inescapable claim to some kind of loyalty. Indeed, blood being Thicker Than Water may be the reason why they still associate with these family members at all, despite all the stress, anger, and danger of looking bad. Inversions of the trope are not particularly noteworthy; lots of people, in reality and in fiction, are cold and reserved with most others, but show affection to their families.
Sibling Rivalry or an Oedipus Complex may be the original source of the conflict (depending on the actual relationships involved, of course). People mostly grow out of those sorts of problems, though, or try to avoid looking too bad as a result; this trope can kick in when a good person lets a family conflict turn toxic. Abusive Parents can of course be an excellent reason for not getting on with one's family; merely Amazingly Embarrassing Parents can also trigger the trope if they don't let up on the habit when their kids leave home. The Glorious War of Sisterly Rivalry or a Cain and Abel situation can generate this trope if either or both of the siblings looks nicer when out with friends and not engaged in the conflict. If the problem is a seriously Dysfunctional Family, an Archnemesis Dad, or an Evil Matriarch, the character may get special credit for getting out of that mess. Conversely, a dark version may arise when an Antagonistic Offspring finds allies.
Family of Choice avoids this problem by having "family" actually be chosen friends - though once somebody is committed to a Family of Choice, they may feel unable to drop them despite a breakdown in the friendship, bringing this problem back into play.
- One Piece: It's a running gag that Luffy hardly even knows about his family, let alone their infamous reputations, while he shows the utmost care for his friends.
- Fairy Tail: Erza and Natsu don't have great luck with their relatives (Natsu's brother is the Big Bad, while Erza's mother is The Baroness and her father is guilty of Van Helsing Hate Crimes). Luckily, they consider the rest of the Fairy Tail guild to be their family, and don't consider their blood relatives to be family members to them.
- A famous joke from East Germany:
Teacher: Fritzchen, why are you always speaking of our "Soviet brothers"? It's "Soviet friends."Fritzchen: Well, you can pick your friends.
- Alexander Tagere from the Arcia Chronicles has the best friends a man could wish for: a tightly-knit group of young nobles who view him as their leader and dub themselves the "Wolf Cubs", after his personal coat of arms. His family, on the other hand, is Big and Royally Screwed Up, starting with his mom, who hates him, through his middle brother, who fears and despises him, all the way to their distantly related rival clan of Lumen, who see him as the devil on earth.
- Several of the more likable princes of Amber in The Chronicles of Amber must appear this way to their friends in Shadow. The problem is, they're part of a family of superbeings who've been plotting against each other, sometimes viciously, for centuries; turning paranoid and ruthless, even brutal, when family show up, is a basic survival mechanism for them.
- Some of her friends and colleagues are perhaps a little surprised by Angua's reactions to her family showing up as part of the plot of The Fifth Elephant, although they get the point soon enough; she's the White Sheep in a family of man-eating werewolves.
- From most people's point of view, the D'Regs in Jingo are a whole nation that embodies this trope. They are violent, sneaky (but not totally stupid) desert raiders; they have their own idea of honor and rules of conduct, but they pride themselves on being untrustworthy. One of them says that his mother would be horrified if she thought that he trusted her.
- Harry Potter
- The title character is very good at making friends with all different kinds of people, but his relationship with his only close living relatives, the Dursleys, is very bad. (His parents loved him deeply, but they're dead.) This doesn't reflect badly on him, though; they're shown to abuse and bully him in the early parts of the series, when he's still a child, but he doesn't retaliate (much) even once he becomes aware of his magical powers. And according to Word of God, he and his cousin Dudley, who underwent a Heel–Face Turn after being attacked by a Dementor, do develop a normal cousin relationship as adults.
- Sirius Black was the White Sheep of his pureblood-supremacist family, and was far closer to his school friends than any of his immediate relatives. By the age of seventeen, he got so sick of his family's rhetoric that he just left and went to live with his best friend.
- Jeeves and Wooster: Bertie Wooster is fundamentally incapable of turning really nasty, and definitely believes that blood is Thicker Than Water, but the appearance of once of his bossy aunts can drive him to, by his standards, desperate measures.
- Simona Ahrnstedt:
- This trope is zig-zagged when it comes to Beatrice in Överenskommelser. It is averted with her cousin Sofia, who is one of her best friends. But when it comes to her uncle Vilhelm and her other cousin Edvard... Well, let's just say that they are evil abusive sociopaths.
- Illiana in "Betvingade" is the White Sheep in a Big, Screwed-Up Family, so it's no wonder that her relationship with them (except for maybe with her twin brother, who dies at the beginning of the novel) is bad.
- Better Call Saul: Chuck is a highly respected lawyer with a strict ethical code. At work he is seen as a Reasonable Authority Figure. However, when it comes to his brother Jimmy, Chuck can be utterly unreasonable, vengeful, and petty. This is partly due to Chuck resenting Jimmy for being The Favorite, and partly because Jimmy has done some very bad things in the past that Chuck just cannot forgive.
- Star Trek:
O'Brien: You choose your enemies, you choose your friends, but family? That's in the stars.
- In Star Trek: The Original Series, Spock has a very good relationship with his crewmates (particularly Kirk and McCoy), considering he's culturally required to be The Stoic, but he has severe issues with his father, to the point where they didn't speak to one another as family for almost two decades. Stories involving his family show a different and troubled side to Spock.
- Star Trek: The Next Generation then partly inverts the Spock situation, possibly to the point of conscious parody, with Deanna Troi, who is sensitive and empathetic to a fault; the episodes where her meddling mother, who is all too happy to speak to her, shows up at least allow her to show a little bit of irritation.
- TNG also brings this up in "The Icarus Factor", when Will Riker's father, Kyle, shows up on the Enterprise after years of the two not speaking to each other.
- Hamlet is a thoughtful, academic fellow who has friends both close and distant, and a developing romance with a girl who has even stronger feelings for him. Unfortunately, his uncle turns out to have murdered his father and married his mother. Everything goes downhill from there, as Hamlet turns into a ruthless avenger despite himself.
- Bobbinsverse: Ryan Beckwith tends to react negatively to his father. This doesn't make him look bad, though, as the mild-mannered Ryan is quite polite about this, and his father is, depending which of the strips you read, at best a feckless tramp, at worst a career criminal who almost dragged the young Ryan into crime. Ryan's mother responds to her husband with outright violence, because she's fiercely protective of her children.
- This trope is something of a theme of Dumbing of Age:
- Both Becky MacIntyre and Joyce Brown are in the process of breaking away from Christian fundamentalist upbringings to more broad-minded world-views, making friends with non-fundamentalist fellow college students in the process, which leads to serious friction with their still-fundamentalist families. Whereas Joyce is on a long, hard path of change, so that her relationship with her family is merely difficult and complicated, Becky breaks away radically, coming out as lesbian and abandoning creationism — and her father responds by bringing a shotgun to the college. Becky subsequently shows a definite understanding of the trope.
- Amber's relationship with her father is violently negative, to traumatic effect for some of her friends. When Joyce describes her as "as good as family", she doesn't take it positively, and she even has a comeback when Joyce asks what's wrong with "family" you choose.
- Ruth only fails to illustrate the trope because she doesn't really do friendship much.
- Girl Genius: Agatha definitely has this dynamic with her maternal side of family sans Theo, the other White Sheep. The paternal side is just as bad, but because her missing father and uncle are the last two Heterodynes before her generation, it's not mentioned much.
- Go Get a Roomie!: The normally rather chilled Lillian gets downright neurotic, even paranoid, when her mother unexpectedly visits, while Roomie doesn't even mention her family for quite a long time.
- In Shortpacked! (from which Dumbing of Age, above, draws some of its characters), one of Robin's lifelong goals is to live this trope, as her family life growing up wasn't particularly happy. It's spelled out here.
- Sticky Dilly Buns: Ruby Larose can be abrasive or manipulative with strangers, but that seems mostly to be a defense mechanism; pretty well every other cast member manages to get through that shell and takes a liking to her, while she soon learns to appreciate their friendship. Unfortunately, almost every time she has to deal with her sister Amber (which is often, as they're sharing an apartment and Ruby becomes Amber's PA), her long-standing bitterness (which has a quasi-Freudian Excuse) comes to the surface, and Ruby turns brutally sarcastic and hostile.