In the UK it is almost universally an option to use either 'Mx' or no honorific. Most people will miss this, (no pun intended) because they wouldn't ask about it, however, only once in the last 2 years have I met with a situation where I had to put down a gendered honorific. This is possibly because most organisations that ask for your honorific tend to be of a more formal nature, and so are well thought out.
Places that use 'Mx' have included banks, train & flight companies, loyalty cards, utility companies and components of the NHS.
Not all organisations deal with this issue using 'Mx' though. As I mentioned earlier, some organisations are happy to simply omit honorifics, both my Internet provider and my place of work deal with it this way. As I am only drawing from personal experience, I don't know which is the more common approach.
As best I know, the only significant place where you still are compelled to identify your gender is your passport. Although the document uses the label sex, it probably means gender as a CGR is what's required to change it. A UK passport does not record an honorific, so it does not really count in this question.
As for when I first saw it, I can't honestly remember. The oldest document I can find it on at the moment is my rail card, which is only from 2013. The last time I remember its absence, however, is Facebook, who did not update their options until 2014.
I pronounce it mix as the few times I have heard someone else say it (when signing up for something over the phone) that is how it's been pronounced. It's an unusual thing to actually need to say.
Seat hog
Without having an example sentence, it's hard to suggest a perfect fit, but I would suggest "seat hog" or "seat hogging."
There's even a whole blog dedicated to posting pictures of this sort of people. (I tried to pick a photo with a non-obvious gender)
From that blog:
SeatHog – noun – \ˈsēt-hog\ – a selfish or clueless individual who deprives another individual of any reasonable or unimpeded opportunity to sit down.
(In my dialect in regular IPA: /ˈsi:tˌhɑg/
)
The sort of picture they share:
Washington state's Sound Transit* uses "seat hog" to teach people how to ride the train. (Included the other ones because they're cute too.)
For readers unfamiliar with this use of "hog," it follows this OED definition:
[6] b. orig. U.S. Chiefly with modifying word: a person who appropriates or monopolizes something in a greedy and selfish manner. Cf. hog v.1 7b.
- Seattle metro area, the "Sound" refers to the Puget Sound, which lies directly west of Seattle.
Best Answer
Birth name is completely gender neutral, but it might be confusing out of context.
Pre-married name will provide context in addition to being gender neutral.
Or even née and né which are derived from French meaning born. They are past participle of naître (to be born). But, as most Americans wouldn't recognize né as masculine and née as feminine, it retains some of its neutrality. You would still need to designate male and female properly for those who do, but it won't be as loaded as "maiden name".