A term used by people who are tired of calling n00bs "idiots".
The individual calls a n00b an "idiom" so that they'll get even more confused and react in a more n00bish way. It will confuse them until the n00b actually looks up the word in a dictionary to find the definition. Otherwise, they'll think idiom is another word for idiot.
n00b - "FucK ALl YoU BItCHaSs WanKsTaZ"
John - "stfu you idiom"
n00b - "iDiom? FuCK YOu, YouR AN iDioT"
John - " *Shakes head* "