Well, those things are harmless to others, but they aren't harmless to you, because bad manners may result in people avoiding you. These are all signs of disrespect, that you have no care for the feelings of the people around you. So they will probably respond in kind. You may "get away with it" while you are a child and living with your family, but i doubt people will want to join your lunch table at school or work. Employers often take a prospective hire to lunch just to evaluate their table manners, so there's that. If your parents didnt teach you, find an etiquette guide book or online.