tactical retard

a person who uses the same tactic every time even though it usualy fails

People (gamers who play Online Mass Multiplayers, in particular) who seem to play without any coherent idea as to what they should do, and remain oblivious about the positions of their team, the enemy, or even complete functions and aspects of the game they're playing.
Their gameplay is so atrociously bad, that it gives the impression they suffer from Attention Decifit Disorder, or have never even heard of computer or video games until that very moment, despite having played the game a couple hundred times by then.
In most cases, they're completely detrimental to the team, dying early on without contributing much, or even hindering the game for others.
In the rare occasions they're actually helpful, it's more by accident than by willful act from their part (i.e. acting as cannon fodder, or spotting enemies and giving them something to concentrate on)