A person who has zero or minimal friends. One who isn't usually accepted by the majority of society. A person who has a lower intellect than the "normal" people. YotKon's usually spend most of their lives doing or partaking in one activity.(computers, etc.) A YotKon usually is fairly unattractive and sees this certain activity as a refuge from the "normal" world.
Characteristics: May be pale, unattractive, a bore/freak to "cool/popular" people, girlfriend-less, etc..
That guy is a true YotKon.