What kind of lunch etiquette would be considered bad enough to the point where you think it should affect the hiring process? Do you mean like holding a fork in your ahand in a way someone would consider improper or something more disruptive? Where would you say, when it comes to behavior during lunches, that you would draw the line such that crossing it is legit disruptive?
I have been at business lunches where people were so offensive, I would not work with them. As an example, I was at a business lunch one day and one of the people I was eating with reached over and took food off of my plate and ate it. I could not believe it!
At a business meal, I intentionally slow down and eat slowly. Generally speaking, eating fast does not inspire confidence or make the right impression.
Dining etiquette is in the details. Ordering the right kind of food as not to have a manners nightmare, like not slurping spaghetti, or that over-sauced burger and insisting on using your hands, or not using your napkin.
Manners as my earlier post states is about respect.