Both my parents and grandparents were very strict on having good table manners.
I’ve always been pleased they were as I’ve never been worried about eating in public or wondering what different cutlery etc is used for.
It’s now the same in my family home and I’ll admit I love my dining table at Christmas/Dinner Parties when it’s all beautifully laid out out with appropriate cutlery for the courses, napkins (linen of course 😃) and tableware.
My DC and DSC have good table manners (even if they grumbled occasionally at having - oh horror - to sit at a table to eat and use appropriate cutlery, using the appropriate hands).
But now even they have seen the light as young adults and when eat out/in company and are pleased they know the drill.
Like the OP I really dislike poor table manners.
I can get over the American style of eating tbh or even holding a knife like a pencil (but why???? The point here isn’t so much manners as the correct way of holding it allows you to control the knife better and cut more easily). I grates me a bit but different strokes and all that.
It’s the hoovering food, mouth open, licking cutlery/plates or giving it to your dog to do so, dogs in restaurants full stop, bending head to plate rather than cutlery to mouth, shoving huge portions in the mouth so a person looks like a open mouthed hamster, being rude to restaurant staff, noisey sucking/chewing, belching, grabbing food to excess - that won’t be eaten - in buffets, slathering food in salt before even tasting, dropping food on the floor/letting your children throw food around and not picking it up, screaming children running around and last but not least asking for bloody tomato ketchup in a Michelin Star restaurant to put on a diver sourced scallop.