So many things.
The assumption that everyone likes surprises, celebrations and going on holiday and you're miserable or a killjoy if you don't.
Children are routinely told it's rude not to look at someone when they're talking to you, to fidget, or to question anything an adult tells them as fact.
The whole concept of uniforms or dress-codes.
The use of metaphors and idioms which is so widespread and ingrained that most NT people don't even notice they're using them half the time.
Being expected to "read between the lines" in a conversation, being expected to recongise sarcasm, or know when it's your turn to talk or when a conversation should stop.
Job interviews that heavily weigh first impressions rather than skill or competence, where you're often expected to engage with tasks or questions that are specifically designed to see how you cope under pressure.
Bright lights, background music, crowded spaces, or strong scents are considered "normal' in most public places when Autistic people may find them overwhelming or even painful.
Workplace norms that often disadvantage ND people who can find themselves overlooked for promotions due to less conventional social behavior despite performing well in their jobs.
Fussy eaters in adulthood being labelled as childish or pathetic and the assumption that this is something people should "grow out of". If you're being hosted it's seen as "rude" not to eat what's put in front of you. There are many behaviours that are seen as "childish" because they are not the norm for NT adults but are not at all unusual in ND people.
Our entire education system from the curriculum, to the physical environment of schools, to school events and methods of assessment. So many bright Autistic kids underperform in exams because they interpret the questions literally or aren't able to read between the lines. I remember my DD (who is very academically capable) having a panic attack when she was asked to write a poem "from the point of view of a storm". Her brain simply could not compute how weather could possibly have a point of view.
I could go on all day to he honest.