A console fanboy is a person who consistently claims that one video game console is better than the others, and insults anyone who plays one of the consoles he/she hates.
Ironically, anyone who calls someone else a fanboy is usually a fanboy themselves. An overwhelmingly common behavior in console fanboys is to call someone else a fanboy, and display fanboy behavior immediatly after (see example).
Unfortunatly, the term gets thrown around so much that few treat the word correctly now. Someone who says he prefers one console over another is immediatly called a fanboy. The most commonly forgotten fact is that fanoys are people who mindlessly trash another console and the people who play them for no reason, NOT people who are just expressing an opinion. Few actually take the time to tell the difference.
Example of the "Calling someone a fanboy and behaving like one right after" behavior:
Sane poster: PS3 and Wii are fun, but Xbox is my favorite.
Console fanboy: OMG us such a 360 fanboy!!! 360 fanboy alert! PS3 is better than both consoles, better graphics, better sound, better online, the other consoles are so shitty, it's unbelivable! PS3 is the ONLY good console, i say SWAT teams should execute anyone who plays anything else! God, stop being such a 360 fanboy!!!