I’m going to go waaaaay out on a limb here. Shoot me down in flames if you like.
I don’t think putting your elbows on the table is bad manners any more. I remember being told not to put my elbows on the table when I was a kid, but I think times have changed.
We’ve moved on. We can now put our elbows on the table in even the finest restaurants, and nobody will stare. The maitre d’ won’t have us ejected. It’s not rude anymore.
Spitting and picking your nose at the table? Yeah, that would still be rude.