A person who is addicted to using internet relay chat.
People who, for the most part, drink a lot and do illicit drugs. Many irc addicts drink enough to kill a mule, while typing for as many as 20 straight hours, into ircchat rooms.
Irc addiction is just a state of mind. Some snap out of it after a few months and others just can't shake it. It's kinda like crack for smart people.