Well, my grandfather used to say in cases on 'no, not really', where table manners were concerned, to 'keep it for the dining car'. I guess, as he was born in the 19th century, that trains in those days did not run very smoothly, thus you had to / were allowed to do things you wouldn't be permitted otherwise, like dunking bread or resting the bottle on the rim of the glass.
Anyway, whenever we, as kids, would do something not totally 'off', but 'reprehensible', we were told that we were not in the dining car.
Once we had dinner at a medieval restaurant. My then third grader had been entertaining the whole family by telling us about the table manners of the people then (largely none). When we got there, I immediately told them to apply medieval table manners - their faces lit up (great hit, cool, mom) and we spent a weird evening with the best food of my life (if you didn't mind holes in the table for holding the mugs and the occasional flying bits of food) and entertaining attempts at eating crayfish soup without tools - table manners, yeah!