My favorite gender joke: A little English boy is shown a picture of a naked man and a naked woman and asked to identify the boy and the girl. He replies, "How should I know, they haven't got their clothes on!"
But it took watching my kids grow up for me to become aware of how naive I was about gender. When my daughter was two I was play-quizzing her about who was a boy and who was a girl. Her answers on one level were right on (but sometimes, though she got the genders right, she got the sexes wrong). For example, she guessed my mother was a man. Anyway, she picked up on my "shock" at some of her answers and she became hyper-sensitive about gender for a good two years. She started insisting on wearing hyper-feminine clothes/jewelry/ruffles/etc. I realized that I had created this situation, but figured that it would work itself through and out....which, eventually, it did.
Joanna