Well, it's a multifaceted demand, so I'm going to forget many good examples.
If you hear any casual remark about boys needing blue, girls in pink....boys do the handiwork, boys will be boys, boys are rough, girls are smarter, any remarks about male occupations, female occupations. What a man does as a gentleman, what a woman does as a lady. There can also be differences in how an instructor reacts to a situation if it is a boy or a girl student, like "toughen up" to the boys, and a bit more reassuring with the girls, perhaps protective.
It might not be as memorable as a specific lesson plan and course objectives, but that's the quality of social expectations...less noticed than expected.