Young people on Tumblr-- I associate this behavior with the sort of online fandom, queer, and social justice commmunities that care very, very much about Performative Wokeness. "Ask someone to tag for a highly idiosyncratic trigger on their Tumblr and then scream at them for being ableist rather than unfollow when they say they can't do that" seems to be the latest trick from the same people who were already doing things like demanding people writing fic with abuse in it share enough of their trauma history to prove they're traumatized enough to deserve to write such things.