I grew up a military brat, so I am well aware that different areas of the country, and different cultures have their own rules of courtesy for parties and events in the home. I have had long discussions with friends on how the South and New England have their own versions of Emily Post manners.
Now, let me relate to you some experiences I have had with a particular acquaintance, and see if there really are areas of the country where these would be considered good manners.
When invited over for a dinner, where I made home made spaghetti sauce and my own fresh bread; this person showed up with a grocery store loaf and garlic butter, and proceeded to made garlic bread in my oven. No, didn't ask permission, and had been told not to bring anything as the dinner was planned. This is besides the fact the cheap garlic butter that was used made my whole house reek for days.
Recently my college age son decided to have a Halloween party, which we told him we would help him with. This acquaintance is dating the mother of some of the other college age kids coming. I get a call as I am cooking some party snacks, they want to know what the menu for the party is. (um, THEY weren't invited) When the college age fare was related (pizza, munchies, chili, cupcakes and brownies) I was informed they didn't like any of that, and wanted to bring their own steaks over to grill. They were informed we weren't starting our grill up for them, and I figured that was the end of it.
Since the party started after 5, at 4 I was finishing things up before I jumped in the shower. I get a knock on the door, there they are, with the 10 yr old son whom they informed me they were dropping off at the party while they go out. While I absorb this, I am informed I am cooking the chili wrong also. The evening went down hill from there.
This is just two examples of a long string of incidents. (yeah, I don't invite them to anything any more) Now where I come from, we would say this person was raised in a barn. What do you say?