This is a massive fandom pet peeve of mine that I've literally never talked about. Yanno how people use headcanon refer to anything anyone thinks a certain character would do? Well thats not what it means.
A Headcanon is something that a character would do that does NOT contradict canon.
Headcanons are things that someone who has consumed that piece of media can hear about and go there's nothing in canon to disprove this, so even if it isn't stated it could hypothetically happen so maybe the character did do this but it was just never talked about.
A headcanon is something like Frankenstein having bolts-canon never says it but canon also never not says it.
For example, saying you headcanon a character is gay when they have canonically been shown to be attracted to the opposite gender is not a headcannon, because canon disproves it. Saying that a character is bi or pan or multisexual when they have canonically been shown to be attracted to the opposite gender is a headcanon(just because they have been shown to like one gender does not mean they don't like other genders).
Similarly you can headcanon a character as having transitioned into their canon gender but only if there's no canon depiction of them as a baby or toddler where they are the same gender they currently, canonically are(because that would show that they are cis).
This isn't just about sexuality or gender, but also about things a character's likes or dislikes and habits. I've seen so many people depict in fics and/or headcanon a character who mainly uses non violent & defensive strategies in fights but bcz its never really pointed out by the narrative and also bcz they are often verbally aggressive, their dislike of physical violence has been ignored, and its common to for them to be depicted and/or headcanoned as violent and physically agressive.
Another example is if a character canonically has been raised by their parents-even if it's proven by a single one off line or something the creator said in an interview-and then you headcanon them as growing up in an orphanage, is not a headcanon, because it actively goes against canon.
Another thing is things that are implied to not be canon being seen as a headcanon. For example, if a character is implied to be poor as a child and you headcanon them as being raised rich, then you either need an explanation for why they did or said whatever implied that they were raised poor or it's not a headcanon.
I think fandom needs a new word for stuff that people want to believe about characters that contradicts canon and/or implied canon. Oh wait, just realised that's called ooc but no one likes saying they like an ooc version of character bcz then they have to admit to mischaracterising a character or not actually liking the canon character so i still sorta think we need a new word.
