I haven't gotten the offensive query "why are you like this??" in some time, but when I did - pre-diagnosis at age 27 mostly - I just brushed it off with a rather flippant retort or with another question.
e.g. "why do you judge?" or "why is anyone like anything? what does it matter in the end??"
Yes, it's kind of perverse yet philosophical and nihilistic...but the subtext, as I hoped the, ahem, NT would pick up is that the matter isn't up for discussion, just drop it and move on to another topic. But they usually kept pressing the line of inquiry, which is in large part what compelled me to seek a formal diagnosis. This was years ago, before I even knew what Aspergers WAS. I was relegated to telling them that I had "a form of ADHD with social anxiety" as the so-called professionals told me.
The subtext I always read into that abrasive query was "why aren't you more like ME?" or "why don't you get obvious things that other people get?" - I suppose with the wisdom I've accumulated since then, I would've replied not with a question but "Well, that decision was made by someone at a much higher pay grade than you or I" - regardless of religious beliefs, I think that's a pretty good retort 