How do you teach someone to be more socially able?

My boyfriend’s a gamer, and he seems to not understand things that we should’ve learnt before.
For example, he stands in front of the door as people are getting off the bus, and says that they can just ‘walk from the side.’ and I think we should understand it really isn’t that they can’t walk from the side, but that its rude?
Another example is that he doesn’t attempt to strike a coversation when he comes to my house, and just games on the computer. After dinner, or after he finishes, he just says he is full and goes back to the PC, rather than stay, and strike a conversation.
My mom has a really bad impression of him already, and me and my sister have no idea how to solve it. Help. please?