If you're not familiar with headcanons, this card explains the fandom phenomenon. The short version: some fans like to imagine circumstances or character traits that are outside of the accepted canon. That's why it's a 'headcanon', it exists inside your head.
I headcanon Sherlock Holmes as genderqueer.
The definition of genderqueer varies. Some people feel that their assigned gender doesn't suit them, so they choose to identify as genderqueer. Other people are undecided, and identify as genderqueer in the meantime. Some people use this identity because they reject the gender binary entirely.
Whatever the definition, there's almost no nonbinary representation in the media, which means that nonbinary and genderqueer fans need to turn to each other to create the representation they need. The Sherlock fandom in particular has embraced this, reimagining Sherlock Holmes to identifying as genderqueer.
(Fanart by damn-it-darcy)
(Fanart by cumberlocked)
Genderqueer Sherlock and Punk!John ftw
I don't really remember where this headcanon came from. I don't personally identify as genderqueer, but I also don't really buy into the gender binary. If anything, I feel like I identify as "female-ish", and I prefer either she/her or they/them pronouns.
I think what appeals to me about this headcanon Sherlock's notoriety. He's one of the most famous literary characters of all time. He's always been a bit odd, but the things that make the character strange are also what makes him special. I think it's a nice metaphor. Sure, being genderqueer, nonbinary, or genderfluid isn't the norm. That doesn't make it bad or wrong. We should appreciate people who are different the way we have appreciated Sherlock Holmes for years.
The above fanartists imagined Sherlock Holmes as AMaB (assigned male at birth) experimenting with clothing that is coded as 'feminine'. My favorite fanfiction 'Image of a Man' by reckonedrightly imagines Sherlock Holmes AFaB (assigned female at birth) presenting as male, and not quite sure how to identify (the fic takes place in Sir Arthur Conan Doyle's universe so the character wouldn't have had the same felxability with language as we do today).
Being assigned a specific gender doesn't dictate who you are.
I don't know anyone who didn't get a gender assigned to them when they were born. If you still identify with that gender, that means that you are cisgender. If you don't, or maybe you do for now but are questioning, there are other options for you to consider. Part of the beauty in queer headcanons is that you can imagine characters that you relate to experimenting, giving yourself the space to do the same. That's not necessarily what everyone is doing obviously. I have queer headcanons because there's a scarcity of queer canons.
Even when there are queer characters in mainstream media, they're often really freaking sad.
And it's really unfair. Sure, all stories need conflict, but how many queer characters get happy endings in the stories we tell? When so many LGBT kids are suffering from depression and committing suicide, it's really frightening to consider the fact that the message we're sending is that there's no future for them. We can do better. I'm glad fandom is stepping up.