God, this is a tight race. Guess it's time for propaganda part two.
Candace's summer has sucked. She's been dragged onto her brothers' dangerous inventions despite being terrified of them, she's been turned into various things against her will, including a fly and a liquid. She's been attacked by animals, stampeded by cows and humans, accidentally got high once while lost in the middle of a forest, and regularly falls from high places. She had hair grow all over her body on a date and her boyfriend's mum tried to shoot her with a tranquiliser dart because she thought Candace was an orangutan. Her boyfriend's psychopathic little sister put squirrels in her pants (giving her a fear of squirrels) and trained her dog to attack her.
And worst of all, rather than getting acknowledgement that any of this actually happened, her mum thinks she's insane because everything vanishes into thin air before she sees it. The universe is genuinely against her.
And how does she feel about that? Well, how do you think she feels?
Once again, these are all canon lines and scenes.
Her brothers can do anything and everybody loves them, leaving her feeling overshadowed and irrelevant.
And indeed, Candace has attempted to run away from her life and society three separate times (in two episodes and one movie). And who can blame her? Her life sucks.
Candace mostly just wants her mum (Linda) to believe her and appreciate her, but usually, she just gets in trouble, made fun of, or ignored. Even Linda's apologies are backhanded:
In the episode "Mom's Birthday" she's trying her absolute heart out to do something nice for Linda's birthday and P&F outdo her at every turn while everything she makes gets destroyed. The breakfast she prepared for Linda gets slammed in her face without Linda even noticing, the cute dress she bought as a present gets eaten by moths, she eats her own card because she thinks it's inferior to what Phineas and Ferb made, and all her musical instruments disappear so she can't play the song she wrote.
And then even the happy ending of that episode where she finally gets a moment in the spotlight, it lasts all of five seconds before Phineas redirects her attention away gain.
Candace has a whole collection of depressing-ass songs, too. In this episode Candace's personality gets split into two and they sing a song about how much they can't stand one another. It never gets resolved either, they get merged back together without reconciliation and it's clear she's just as much at war with herself after this episode as she was before.
The worst part is, there will never be a lasting happy ending. Because if Candace is happy then the show doesn't work, and Disney will never let the show go. Even in the 20-years-in-the-future flash-forward ep Candace relapses the second she sees the boys, suggesting even in all that time she never really gets over it.
Papyrus is indeed capable of saying fuck and may or may not be willing to, but he is a kind soul and would willingly give it up as he would recognise that Candace needs the fuck far more.