I just skim read the previous thread and it gave me the creeps. There is a culture difference in my family too (DH is British, my family are not), and there is a culture of male chivalry in my country that DH just lacks.
Examples: First thing the men do when they walk into a room in the evening, is check whether anyone wants a drink (women never pour drinks). DH seems to think he's a guest, and sits about getting waited on.
If the women have gone grocery shopping, men come out to help carry in anything heavy. Doesn't even occur to DH. I have to ask / tell him to do it in the UK.
Going on a long journey: men tend to pack the car boots, fetching and carrying heavy items from the house. DH sits on his arse (in the UK I pack the boot because he's useless at it).
A man would never walk through a door ahead of a women; DH thinks nothing of it.
The one that embarrasses me the most: when food is being served and there is a crowd, children get served first, then women, and the men go last. At Christmas, I turned around to see my DH cheerfully piling his plate high while the women and children waited, and the men were standing back chatting, watching and waiting. First in the queue. I have spoken about this to him before, and his logic is the men take too long and their food gets cold.
I see it all and it embarrasses me. I don't notice it as much in the UK because chivalry is a bit dead here, and he's one of many. But crikey, in my country he comes across as seriously rude and lazy. I am slightly irritated with him the whole stay, and that irritation eases when back in the UK.
My point is, your daughter already knows what her bf is, because you raised her and she knows how all your family and friends behave. She shares your values. She's in denial about her bf, or hoping you haven't noticed.
If you gently tell her you felt taken advantage of, don't like the way he talks to her Dad, did not appreciate him going into your bedroom or helping himself without asking first etc, then she'll know you've seen it too. It won't be a surprise. She might be miffed you won't participate in wilful blindness, but too bad. It's her job to manage the relationship between you and him, not yours ... she's the common link. You need to set boundaries though, and be very clear about what you do and do not expect.
In my case, my DH gets his ass handed to him every time ... by me. Imagine fierce whispers: "All the men are fetching and carrying and packing the car ...move your arse and help please !"
I also have massive mental load to anticipate his lack of chivalry and warn him in advance: "When we get to 'x' do NOT sit down until all the women and elderly are seated first. If a woman walks in and there isn't a seat ... stand up and give her yours." I do get push back: "That's just stupid / sexist etc". My response is "My country, my family, my rules...". Your daughter needs to do the same.
Finally, I've told my mum and sister I've noticed it all too and it embarrasses me. They haven't raised it with me ... I got there first. I explained things are very different in the UK. I think they feel a twinge of sympathy for my DH whenever he slips up because they know he's probably going to get told off by me when we're alone.
Having said all that, I think there's more to your daughter's bf than just a culture difference. I'm afraid he sounds like a bit of a creep. Watch him closely. And maybe calling this out now will help your daughter to see him for who he is, instead of everyone supporting her denial by participating in a delusion that there's nothing odd about it.