Call me big master pimpin’. I will request you be fired if you do not

It has barely any history prior to 10 years ago. Just because some nobody said it once in the 1970’s doesn’t mean its been colloquially around for 50 years. The source of it “being around from the 1970’s” is a dubious article written in 2015. https://www.telegraph.co.uk/men/the-filter/11597192/Whats-it-like-to-be-a-Mx.html

That’s a name, not a title. You don’t get to choose titles, they reflect objective truths.

Ms/Mrs/Mr all reflect objective truths. Mx reflects how the person feels.

You don’t have free speech in a childrens class room.