Netiquette is etiquette for the internet. For those of you that are new to the internet, especially to chat, you might want to know what is considered polite behavior. Typing in all or excessive capital letters is considered shouting and therefore seen as rude unless it is necessary to the content. It is considered polite to say hello to everyone that enters the room. People who aren't welcomed with a hello often feel ignored or unwelcome.
People try to make every effort to say hello.
But sometimes things happen. It is considered polite if you make an effort to say you are leaving the room before you leave, otherwise other people sometimes wonder if they said something wrong to cause you to leave. Given the nature of IRC, sometimes it is just not possible to say good bye before you leave. But an effort is all that is asked. Like in real life, the Golden Rule applies here.