I think there is a strong need for binaries and categories, something ingrained in the human psyche. And with gender, I think it scares people not to have the stark contrast. I find it in myself more often than I'd like and try actively to challenge its existence. But a lot of people don't give it a second thought.

With my son, I would get defensive at the "girl" mistakes. Which were incredibly common when he was a baby (gorgeous curls, long eyelashes). I finally realized that there was no reason to correct the random person in the store, because it changed nothing about my son for them to think he was a girl.

Why do we like categories so much? Because it makes it easier to make sense of a complex and often senseless world?

We have a neighbor child who is female almost in sex only. Yesterday my youngest daughter said, "Sometimes I forget and think S is a boy." No amount of long hair and pink clothing makes my daughter see her friend as a girl. I find that curious, for all the reasons you enumerate here.

Oh this stuff drives me nuts. Someone walked into my house the other day when Swee'pea was playing with his trucks and pronounced, "Oh he's such a boy!" And I felt the need to talk about how much he loves to pretend to cook and how he nurtures his dolls and stuff animals. People just see what they want to see. Because I dress Swee'pea in bright colours and not in frat boy or camouflage clothing, strangers often mistake him for a girl, but I never correct them unless we're actually having a longish conversation or something.

I've had several conversations with people who try to illustrate how boys really are just different from girls. They talk about how their son is totally different from their daughter. And I always ask them, "Why do you think that's because of their gender? Why can't they just be different PEOPLE???" So far, nobody's ever been able to answer.

Funny, we had a conversation about this just the other day because - at the dentist - my daughter was "asked", "You must like pink, don't you?" I say "asked" because it was imposing rather than questioning and because my daughter answered, "Yes", thereby reaffirming that persons weird belief in that binary equation. Meanwhile, if you ask her what her favourite colour is she will list about eight colours, ranging from black to green (her daddy's favourite colour) and orange (her mama's favourite colour) and, yes, including pink. That, to me, was such a telling interaction.

And, through this, she learns that she must like pink...and if people know that about her just by looking at her, she will wonder why that is and - upon further investigation - learn that pink is for girls and blue is for boys. It drives me crazy. Of course, as a scientist, my first question is, is preference for certain colours biologically determined? Individually, perhaps. Based on physiological sex? I doubt it. And all those questions extend further and further to other gender roles and I can't figure out why the spectrum we see isn't as diverse and beautiful as the colour wheel.

This makes me nuts, too.

My stock line is that there may be biological differences between girls and boys, certainly it is possible, but even if there are, they are drowned out by the huge differences in the way we socialize kids to adopt gender roles.

We've made a big effort to keep all options open for our daughter and so far, so good. She doesn't want to be pigeon-holed.

@NotSoSage,
My daughter sounds like your daughter - generally happy to change her favorite color on a whim and not bound to any particular color. I was so irked when she got the same lesson about pink at the dentist's office the other day. Annoying, especially since this time, it seems to have stuck.

I hear comments like those from the anonymous parent at the party and to cinnamon gurl's neighbor from my mother and mother-in-law especially, and I've learned to say (in a completely even tone) things like, "At the moment, I suppose so. Give her ten minutes."

It seems to me that the options for boys and girls are pretty wide open these days, as long as girls do things in a "girl" way and boys do things in a "boy" way. I've been watching the Olympic track & field events: the women are sleek with incredibly defined muscles and no breasts to speak of -- built like a young man, according to 1950s stereotypes -- and yet they are unmistakably women. I couldn't say what it is about them that seems so feminine to me; but there you have it.

My 4yo wanted to play "dinosaur games" on the internet, so I searched around for some; but about every one she said, "That's a BOY dinosaur game. I want a GIRL dinosaur game." It's not that the dinosaurs themselves were male, just that the game seemed masculine to her. Alien, I think she meant. I'm not sure why.