And it's not just cisgender folks who have this issue. I find myself inappropriately gendering my genderqueer friends far too often, and I KNOW just how important using someone's preferred pronoun is. Unfortunately I start to see binary people as "normal", no matter how hard I try, because there are practically no counterexamples in day-to-day life. The driving force behind the lack of counterexamples is that everyone is so heavily and so constantly gender policed.
But it's also partly because it's a self-reinforcing cycle. People see that counterexamples don't exist, so people don't let themselves come out and be those counterexamples, so the stigma continues. Well, let's get the ball rolling — here are some counterexamples.