An insult rendered in passing against someone who is not present, usually over a breakfast counter.
Person 1: Does DImmortal realize that his user-name sounds like "Dim Mortal"?
Person 2: That's counter-offensive, yo.
A counter-offensive is the term used by the military to describe large scale, usually strategic offensive operations by forces that had successfully halted an enemy's offensive, while occupying defensive positions.
offense,offensive - the action of attacking an enemy.
Counter-offensive - armed force stopping an enemy offensive