Tumblr genders: The personality of those who have no (socially acceptable) personality.
I'll put genders and stuff like self-diagnosed illnesses or whateverkins in a blender, since they sort of overlap in function, specially with things like noungenders and whatnot.
The "kins", the speshul genders. It's all an attempt to convey "I am dependable/charismatic/friendly" in a single word. "I am trans/autistic/PTSD-sufferer, therefore I fight hard! (and deserve pity for I can't control my emotions!)" or "I am kin with this character/animal people likes, so I deserve being idolized equally (RP ok uwu)" or "I am stargender, so mysterious", "fluidgender, such a free spirit", "aromantic, cool as ice lone wolf" or so.
They are the lowest common denominator, only separated from other flavors of deadbeat by having enough money to have residence and internet access. They are trying to replace the effort of being something with a series of labels, believing that it gives them the benefits of pre-established concepts or other people/characters/creatures who were what they claim to be, but without the effort to be like those hypothetic others and concepts.
In other words, for all the talk of speshul snowflake and such, they just want to piggyback on the image of something else. They are bootleg snowflakes, actually. Mass-produced pieces of media-regurgitating fools (or too young to know better) in crystallized form. They are the opposite of what they want to be. They try to stand out the most, but they are still derivative in the end.
EDIT: Oh yeah and bonus points if it works as a "get out of trouble free" card.
Standing on the shoulders of giants, indeed. Like a bad case of dandruff.