It seems like you are making a different point than the other posters. If the majority of a group does not follow an etiquette standard, it is reasonable to say that the group does not hold that standard. Your point that if any group holds an etiquette standard, then that standard exists is true, but is more tangential to the other point that a rebuttal of it.
> Your point that if any group holds an etiquette standard...
Not quite. My original comment was in response to "I see people violating rule X anywhere, even though I was told it was 'wrong'".
All I am saying is one shouldn't be basing their behavior solely on what they see others "getting away with".