@LagneyandCasey ah the good ol shoes off debate. You see I find it rude to ask people to remove their shoes (I'm not talking muddy wellies here) at their house. Incredibly rude. And it's almost always always a when I've got a mismatched pair of socks with a toe poking out of a hole. Making your guests uncomfortable is very rude. I don't know how it's infiltrated here (UK) but certainly wasn't the norm when I was growing up.
Starting your meal before the hostess has picked up her knife and fork is very rude, unless invited to. My DMs partner's children do this. They often Wolfed down their entire course before DM had even sat down. And of course they don't offer to help clear the dishes.
Speaking of which clearing the dishes by stacking them at the table. Hideous!
Any phone usage apart from an emergency when in company is awfully rude.
Being early. God that's awful. Being hideously late nearly as bad.
There are so many. I'll stop now.