Well, my sons are younger (one is almost 4 and the other one is 1) and they're not in daycare/preschool/organized playgroup, so social conditioning hasn't really started yet. So, for me, I'm viewing it from a different angle right now. With them, I'm fighting to protect that androgynous part of them that I believe is central to young children.
For example, my oldest recently picked out some pink Blue's Clues fabric for the pjs that I'm going to make him. He has other pink pajamas and is unaware right now that pink is considered "feminine". He likes pretty things (who doesn't?). He plays with his little kitchen. He was nursing his baby the other day in his sling. He is gentle and affectionate. Some parents try to snuff that out of boys, discouraging them from expressing emotions or freaking out over the like of "pretty things". We try to keep a balanced environment for them.
I am concerned with other people planting ideas in their heads that these things are not masculine or that they are undesirable, you know what I mean. My goal is for them to not be afraid of the feminine side or not to ridicule such things; they are whole people. We all are whole people. That's my sexism issue with sons right now.
I am lucky that my husband is supportive of this and that he models affection, hugging, gentle ways, nurturing, caretaking, etc. One time, in a Gymboree class, my oldest son chose some pink fluffy wings to wear during dress-up time. I think he was about 3. He said he was a butterfly and he was admiring himself in the mirror when the teacher said something like, "If Daddy were here, he wouldn't let you wear that.". Can you believe that?? I don't know what people are afraid of. I guess I don't get it. I really cringe at the phrase, "all boy". Can you be 25% boy? What does that even mean? I know what it implies and I dislike that. I dislike the small boxes that we force ours sons into.
The other angle of sexism wrt sons that I've already alluded to is modeling of caretaking. My husband changes diapers, bathes, cooks. We don't teach gender-divided work. We all share. If my sons can be like my husband, men who are kind and nurturing and equal-minded, then I will feel like we've wildly succeeded. The only thing I could wish for in them that maybe he doesn't do so much is for them to be more expressive of their feelings. I think that's hard for men, based on social conditioning. We talk about feelings a lot and we accept feelings. Ds1 and I were just talking about this today, in light of ds2 crying; I told him that everyone cries sometimes and that's Ok.
My oldest knows that he's a boy, but I don't think he really knows what that means, from a cultural perspective. He has no idea that dolls are not considered boys' toys. He's picked out pretty pink dresses for ds2 when out shopping. I've put barrettes in his hair. He does not presently identify with his gender, because he doesn't realize that it means anything more than having a penis. I'm not sure that he's thought that through either. I love the androgyny and I think that if people left kids alone, that we would see a lot more of that; I think it's natural.
Anyway, as they grow older, of course, we will talk about respecting people and those people include girls/women. We will continue to model and teach how to treat people respectfully and how to respect their body boundaries. As they get older and much more aware, we can talk about specifics.
In terms of how my sons are hurt by sexism, I think it comes out in society's ridicule of some pursuits as being, "sissy", "gay", not "all-boy", etc. Society wants to limit them and push them into the box, all while complaining that men aren't more forthcoming with feelings and respect. It makes you think and I can't figure out what people are afraid of when they fight to make their little boys "all boy".