Perhaps I'm misreading you, but you seem terribly focused on the letter, not the spirit, of not quite laws but presumed social rules of behavior. That someone

Perhaps I'm misreading you, but you seem terribly focused on the letter, not the spirit, of not quite laws but presumed social rules of behavior. That someone can scheme up a rationalization for some behavior does not make it right, desirable, or honorable. It's OK to put milk into a coffee you buy. It's not OK to buy one coffee and then drink several glasses of milk. The same goes for seating. Seats and tables are there so people have a place to sit while they consume their purchases. There may be no set rule on how long it should take to you drink a coffee, but this is where people have to be honest with themselves and consider if they are really still finishing up that coffee or if they are now, so to speak, just drinking free milk.