mocking and quoting bigots I've seen so far
:liberalism: turns to 
"you know it's hexbear when the tankie pronoun parade shows up to force pictures of pigshit in front of you!"* real quick
[*this is paraphrased, I can't remember the exact original quote]
Or "so suddenly I'm Hitler because i think people calling themselves Fae gender is dumb"
Or "why should i need to learn a new set of different pronouns for every person I meet?" (this followed two comments after "I'm literally not a transphobe, I work with plenty of trans colleagues who feel safe around me" (average lib being scratched in real time by having to acknowledge neopronouns))
.
All of these shitheads claimed to be allies when they started interacting but our brilliant pronoun tags immediately made them out themselves as the bigots they are who only pretend to be allies because it looks bad to be openly and proudly transphobic
TL;DR: 
I had a student a couple of years ago use it/her which was a genuinely tough one to get used to saying. As with most people, though, it was very nice and understanding as long as you made an effort.
"it" is the one that I have real reservations about, not because of the individual using it, but because it's very much a slur leveled against trans people and queer people generally. I'd be extremely uncomfortable addressing someone as "it" in public bc to any passerby it would probably sound exactly like a big white cis guy using slurs against queer people. I guess I'll just have to deal with it, but I really hope folks will step in to defend me if that admittedly very unlikely situation ever comes up.
Yep, that was exactly my hang-up too--talking that way felt dehumanizing. It was a great opportunity for some self-crit, though, and eventually I came to the conclusion that it isn't my job or place to decide what is and isn't dehumanizing to another human, and that my discomfort with saying it was all on me, not the person. If that's what someone genuinely wants to be called, and feels validated and seen by others using that language, then fuck my own personal reservations about it.