3. Gross eating
A lot of people cannot abide bad table manners. They get offended if someone chews with their mouth open, talks while eating, clangs the cutlery against their teeth, or makes vile noises when masticating.
No one wants to hear the noise of food slopping around inside your mouth or listen to a sound that is reminiscent of someone stirring a pot of soggy semolina. Nothing you have to say is so important that it justifies showing other people the chewed piece of steak you are currently attempting to eat. If you are eating in the presence of other people, it is worth using some manners if you do not want to annoy anyone.