Boycotting a national transport network because their driver called them "Sir" (they are 6ft 6 with stubble) 
Identifying as a "nympho slut chick" on social media and insisting that they are reclaiming the word slut when pulled up on it.
Insisting that they are "100% feminine female biological woman".
Also "reclaiming" the word dyke.
Denouncing all and sundry for transphobia on a daily basis.
They have autism and I'm absolutely CONVINCED this is at the root of this particular obsession/delusion but sadly they've found a whole community online and to some extent in RL who are encouraging it.
And yeah I'm using "they" which doesn't come easy at all. I don't really know what else I can do and still maintain some sort of family relationship. They will one day be my responsibility as our parents had him very late (I'm much older) and they may well never be able to live fully independently. I cannot become estranged but FFS!!