During one Fanfiction.net RP I participated in, there was an antagonist character I had named Gabren who 1) never smiled 2) was quite badass and 3) was rather crazy.
One particular person on there said she "headcanons Gabren as lithromantic aceflux". She proceeded to send me PMs day after day asking me to please please please make Gabbie canon aceflux.
The messages got more weird with time, including a vague statement that "if you make him be romantic with anyone, I'll make my characters kill that character".
Then Gabren got a chief lieutenant named Meriam...who was female. Someone he by all indications was very sweet on despite his stoic demeanor. The person proceeded to go ballistic, claiming I was "killing her headcanons", and that "this destroys Ace/Aro representation in this roleplay forum".
She quit not three days later, after posting a massive call out post that got immediately deleted.