We could just change it to Sex, there is no such thing as non-binary sex.
You might want to reconsider that assertion: Wikipedia: Intersex
. I could also tell you about an ex of mine, but that would be TMI.
Actually, intersex states of various degrees are usually thought to be far more common than non-binary gender ones; they occur at a rate of about 1% according to most estimates, as opposed to 0.2% for gender variance as a category. The figures for both are now increasingly considered underestimates, however, by as much as an order of magnitude in the latter category, and at least some studies suggest that they are roughly equal in frequency at around 2%. I would still say that those figures are misleading, as they don't reflect the multidimensionality of variation - both physical and psychological diversity occur in more than one form - but that's getting too far into the matter at this juncture.
However, I don't really want to belabor the point, either way, as it really isn't relevant for the topic of the site, hence my own relative silence about it here up to now, compared to what I have said in other fora. While I have discussed it at length in the Daily WTF - a site I am not currently visiting for various reasons - as well as the aforementioned WA and similar sites such as Tuckerspawn and the EGS and Rain LGBT message boards, and even have mentioned it in other technical and hobby fora such as Daniweb and Homebrew Talk when it was on-topic, it never really came up here before so far as I know.
Pervy creep that I am (as anyone who has figured out the second-to-last of the Sacred Dis Honors listed in my .sig can tell
), I ordinarily would go along with dchapiesky's suggestion, except that's orientation and libido rather than gender or sex.
Besides, even with a relatively small forum, there's a statistical certainty that there is at least one person who is asexual and we'd be back where we started.
Now, I am pretty sure that the field is just a default part of the phpBB configuration, and that it is simply the case that no one on this site ever really thought about it until now; since it really isn't relevant to the subject at hand, we can probably just remove or turn off the field entirely.
And just to forestall any nasty comments, I will merely point out the likes of Dani Berry, Alexia Massalin, Sophie Wilson, and Lynn Conway.